National Occurrence and
Causes of Boil Water
Advisories in the United States
Report to Congress
Office of Water
EPA 810-R-24-003
May 2024
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Contents
Executive Summary 3
Introduction 4
Boil Water Advisory Background 5
Safe Drinking Water Act 6
Public Water System Types 6
National Primary Drinking Water Regulations Overview 7
Data and Information Sources 8
ASDWA and State Websites 8
Online Searches 9
SDWIS/Fed Data 9
Data Limitations to Identifying BWAs 9
Data Analysis 10
Reasons for Issuing BWAs 10
Category 1. Microbial violation, microbial contamination identified, sanitary risks found, treatment
technique failures, and treatment interruptions 11
Category 2. Long-/extended (vulnerable or improperly constructed source, required treatment not
provided) 11
Category 3. Natural or other disasters 11
Category 4. Backflow events 12
Category 5. Main breaks, distribution system repairs, and loss of water pressure events 12
Category 6. Unknown/not identified 13
BWAs by category 13
BWAs by system size 14
BWAs by system type 17
BWA by source type 18
Conclusion 18
Appendices 20
Appendix A. Acronym List 20
Appendix B. Example Boil Water Advisory 21
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Figures
Figure 1: PWS Breakdown [Source: Safe Drinking Water Information System Federal Reporting Services
(SDWIS/Fed) (Submission year 2022 Quarter 1)] 6
Figure 2: Reasons for Issuing BWAs 14
Figure 3: BWAs by PWS Size 15
Figure 4: BWAs under Category 5 - Main Breaks and Distribution System Repair by PWS Size 15
Figure 5: Reasons for Issuing BWAs by PWS Size 16
Figure 6: BWAs by PWS Type 17
Figure 7: BWAs under Category 5 - Main Breaks and Distribution System Repair by PWS Type 17
Figure 8: BWAs by PWS Source 18
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Executive Summary
The Safe Drinking Water Act requires the EPA to
establish and enforce standards that public water The Safe Drinking Water Act allows states,
systems (PWSs) must follow. A critical objective of Tribes, and territories to receive approval from
a PWS is to provide safe, affordable drinking water the EPA to have the primary enforcement
continuously. When a situation occurs during responsibility (or primacy) for the PWS program
which the water is, or may likely become, if they have established programs that meet
contaminated with microbial pathogens (e.g., the standards set by the EPA to support
Giardia, Cryptosporidium, E. coli, and viruses), a drinking water systems, ensure that drinking
PWS may voluntarily issue a boil water advisory water systems consistently provide a safe and
(BWA) to better protect public health while the adequate supply of water to consumers, and
issues are being resolved. Contamination, or the ultimately protect public health. Where state,
potential for contamination, may be the result of Tribe, or territory has an approved PWS
several factors. These factors include source water primacy program, the EPA provides the
contamination, lack of adequate treatment or national oversight and retains its independent
treatment failures and failures of, or damage to, compliance monitoring and enforcement
water system infrastructure. BWAs may be needed authorities. In this report the term "state"
for a single event or may be needed where refers to a state, territory, or Tribe that has
identified contamination, or the potential for primacy under the SDWA.
contamination, and vulnerability persists and
remediation, such as capital improvements, are
needed. A BWA is a voluntary protective public health measure that the water systems can take until
contamination, or the potential for contamination, is corrected. Understanding the prevalence and
causes of BWAs across the United States can provide critical information on the health and sustainability
of the PWS infrastructure.
The Infrastructure Investment and Jobs Act (Public Law 117-58, Section 50115, November 15, 2021)
requires the Administrator of the U.S. Environmental Protection Agency to conduct a study on the
prevalence of boil water advisories issued in the United States. The legislation requires that the
Administrator submit a report to Congress describing the results of the study. The report must include a
description of the reasons for which the BWA was issued.
The EPA analyzed information collected on the BWAs issued across the United States to identify the
most prevalent cause of BWAs and any trends in PWS type, size, and source. The majority of BWAs were
issued because of main breaks, distribution system repairs, or loss of water pressure events (e.g., power
outages or tank pressure loss) and most of those BWAs were issued as a precaution while additional
sampling was performed to clarify whether fecal contamination, measured as E. coli bacteria, was
present in the distribution system. The second highest category of an issued BWA was for unknown or
unidentified reasons.
The majority of BWAs were at community water systems. Community water systems serve at least 15
connections used by year-round residents or regularly serve at least 25 year-round residents.
PWSs are identified by their source type as either surface water PWSs or ground water PWSs. The
majority of BWAs occurred in ground water PWSs. In a small number of cases the source type for the
systems could not be identified.
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The primary PWS source (i.e., ground water vs. surface water) and the PWS size (i.e., population served)
did not have much of an effect on the number of BWAs issued. However, the specific reasons for issuing
a BWA varied by PWS size. Very small water systems (serving less than 500) had the highest number of
BWAs in categories 1, 2, 3 and 6. This may reflect the continuing challenges faced by very small water
systems in maintaining compliance with the National Primary Drinking Water Regulations (NPDWRs) and
adequate infrastructure due to the lack of technical, managerial, and financial capacities. This also may
be reflected in the number of ground water systems with BWAs compared to the number of surface
water systems with BWAs. More than 90 percent of public water systems serving less than 10,000
people use a groundwater source.
The BWA events were assigned to one of six categories. Category 1 advisories include those issued for a
microbial violation, where a microbial contamination was identified, where sanitary risks have been
found, where there were treatment technique failures, or treatment interruptions. A significant number
of BWAs issued in Category 1 were at very small PWSs (population served <500). This is consistent with
the Safe Drinking Water Information System Federal Reporting Services (SDWIS/Fed) violation data for
the NPDWRs compliance for small water systems where the lack of technical, managerial, and financial
capacity at these systems contributes to ongoing compliance concerns.
Introduction
Public water systems are critical infrastructure that
provide services vital to the health, safety, and
economies of communities throughout the United
States. Although most PWSs typically strive to
provide safe, affordable drinking water
continuously, situations arise that may temporarily
disrupt service or require consumers to take
precautionary measures to protect their health (e.g.
boiling water before use). Such situations vary in
terms of scope, scale, and severity. For example,
routine maintenance or a small water main break
may impact a handful of consumers for a short
period of time, while a hurricane or other natural
disaster that causes widespread infrastructure disruption or power outages may impact hundreds of
communities throughout a state or region for an extended period. When a situation occurs during which
water is or may likely become contaminated with microbial pathogens (e.g., Giardia, Cryptosporidium,
viruses, or bacteria), PWSs may issue consumers an advisory notifying them to boil the water before use
(i.e., a "boil water advisory").
Individual states and local agencies often have
different names for drinking water advisories
depending on the situation. Boil Water
Advisories, for example, may also be called
"boil water notices," "boil water alerts," and
"boil water orders." For the purposes of this
study and report, the term BWA includes all
instances in which a boil water statement is
issued regardless of the regulatory authority
or organization issuing the BWA.
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This report presents the results of an analysis conducted by the EPA on the prevalence of BWAs issued
in the United States during the 2021 calendar year to satisfy the Congressional mandate directing the
EPA Administrator to conduct such a study on an annual basis and submit to Congress a study report
with the agency's annual budget request.
The study focuses on PWSs as they are defined in
the Code of Federal Regulations (40 CFR 141.2).
Water suppliers that are not PWSs, including
households that maintain a private well, are not
considered here. However, people that rely on
private wells at their residences may also consume
water from PWSs at schools, businesses, and other
establishments.
A PWS is defined at 40 CFR 141.2 as a system
that provides water for human consumption
through pipes or other constructed conveyances
to at least 15 service connections or serves at
least 25 people for at least 60 days a year.
Boil Water Advisory Background
PWSs use drinking water notifications and advisories to protect public health, meet federal and state
regulatory requirements, educate consumers, build trust in and support for services and maintain a
positive relationship with their community. Some notifications are solely informational and are not
related to a situation that poses a public health risk (e.g., a notice to inform consumers about
anticipated seasonal changes in how the water tastes). Other notifications, often referred to as
advisories, are used when a PWS or regulatory agency believes that services are or may be disrupted, or
that water quality may be compromised. Advisories may alert PWS consumers to be prepared for an
anticipated event, such as a hurricane that may disrupt service, or instruct them to take specific
measures due to potential contamination (e.g., boil water or use an alternative source of water).
"Boil Water," "Do Not Drink," and "Do Not Use" are three types of drinking water advisories that
instruct consumers to take immediate action to protect their health. Before issuing such an advisory,
PWS, state, and local officials may weigh the potential public health risks against other impacts on
customers (e.g., costs for businesses to boil water or use an alternative source such as bottled water).
BWAs are the most common advisory, typically issued for the potential of microbial contamination
because boiling water kills many disease-causing microbes. "Do Not Drink" and "Do Not Use" notices,
which are less common, are often issued due to chemical contamination and are not part of this boil
water advisory analysis.
To assist drinking water systems and states, the EPA has recommended BWA language (example
provided in Appendix B) that may be included in notices for different regulatory situations. State policies
specify when BWAs are required or recommended1. Further, in some cases the EPA may invoke its
SDWA authorities to require a system to issue a BWA independent of any state policies. In some
circumstances PWSs or the local public health department may issue BWAs at their discretion. Some
BWAs are issued to all consumers served by the water system, while others may impact a sub-group of
consumers who are served by certain sections of the PWS. BWAs may last days, months, or years,
depending on the threat and how the water system is operated. Once the concern that triggered a BWA
1 Although the NPDWRs do not require PWSs to issue BWAs, there are situations for which federal policies
recommend BWAs. Several states use certain provisions in the NPDWRs as triggers for requiring BWAs. BWA
policies vary by state. States are not required to report information regarding BWAs to the EPA.
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has been addressed, the advisory is "lifted" or "rescinded," and consumers are notified that they no
longer need to boil the water prior to consumption.
Safe Drinking Water Act
The Safe Drinking Water Act is the federal statute that protects public health by regulating PWSs. It
authorizes the EPA to set standards for drinking water quality in the National Primary Drinking Water
Regulations; and gives states, territories, and Tribes the opportunity to assume primary enforcement
authority of those standards (i.e., primacy). States, territories, and Tribes can also set and enforce their
own drinking water standards, provided their requirements are at least as stringent as the EPA's
national standards. Direct oversight of PWSs for compliance with NPDWRs is largely conducted by
primacy agencies through the Public Water System Supervisory Program (PWSS Program). However,
even in primacy states, the EPA continues to maintain oversight authorities to ensure compliance with
NPDWRs. The NPDWRs, as they relate to BWAs, the PWSS Programs and primacy agencies are described
in more detail below.
Public Water System Types
The EPA classifies PWSs into three categories based on the number of people served by the water
system and whether the same consumers are served year-round or on an occasional basis. The three
categories of PWSs are:
• Community water systems (CWSs) serve at least 15 connections used by year-round residents
or regularly serve at least 25 year-round residents.
• Non-transient non-community water systems (NTNCWSs) serve 25 or more of the same people
at least six months per year. Examples include daycares, schools, factories, hospitals and office
buildings that have their own water system.
• Transient non-community water systems (TNCWSs) serve 25 or more people per day at least 60
days per year. The people served the water do not need to be the same people. Examples
include gas stations, hotels, campgrounds and restaurants.
There are about 144,000 PWSs in the United States that serve an estimated 330 million people per day
(Figure 1).
6,616,264 , 10,328,829
i CWSs
i NTNCWSs
i TNCWSs
i CWSs
¦ NTNCWSs
i TNCWSs
a) Number of PWSs by Type
b) Number of People served by PWS Type
Figure 1: PWS Breakdown [Source: Safe Drinking Water Information System Federal Reporting Services (SDWIS/Fed) (Submission
year 2022 Quarter 1)]
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National Primary Drinking Water Regulations Overview
The NPDWRs are legally enforceable primary standards and treatment technique requirements that
apply to PWSs and protect public health by limiting the levels of contaminants in drinking water. The
NPDWRs for microbial contaminants reflect a risk-based, multi-barrier approach to control microbial
pathogens as well as public communication requirements. Although the requirements of NPDWRs can
vary based on a PWS's type classification and its water sources, all PWSs are required to:
• Protect water sources by identifying and limiting potential sources of contamination (e.g., loss of
pressure and cross-connections and backflow events).
• Monitor for disinfectant residual (if applicable) in the distribution system to protect against
microbial regrowth and issues in the distribution system that may lead to microbial
contamination.
• Monitor water quality for indicators of microbial contamination.
• Take corrective actions to address potential vulnerabilities and deficiencies that may lead to
microbial contamination; and
• Notify the public of potential health risks.
Drinking water treatment requirements regarding inactivation or removal of microbes are based upon
the PWS's source water and are included in the suite of Surface Water Treatment Rules2 and the Ground
Water Rule. (40 CFR 141 Subpart S). These NPDWRs establish the performance criteria for filtration
and/or disinfection treatment before water enters the drinking water distribution system.
The Public Notification Rule (40 CFR Subpart Q) requires all PWSs to notify their consumers about
significant events related to the water system, including violations of NPDWRs or other situations where
a violation has not occurred when these events pose a public health risk due to microbial contamination.
Each notice must describe the violation or other situation, including the contaminant(s) of concern and
any potential adverse health effects, the population at risk, actions consumers should take to reduce
risks (e.g., boil water or use an alternative water supply), what the system is doing to correct the
violation or other situation and when they expect it to be resolved.
Each violation or other situation requiring a notice is assigned to one of three tiers based on the risk of
adverse health effects. Tier 1 notices,3 which are the most time-sensitive, are for violations and
situations with significant potential to have serious adverse human health effects from short-term
exposure, including effects from microbial pathogens. PWSs must notify people that may use the water
about Tier 1 situations within 24 hours. The EPA recommends4 that PWSs include BWA language when a
Tier 1 notice related to microbial contamination is required, including for the following situations:
• E. coli maximum contaminant level (MCL) violations under the Revised Total Coliform Rule (40
CFR 141, Subpart Y).
• Detection of E. coli, enterococci, or coliphage in a ground water source sample.
2 The suite of Surface Water Treatment Rules includes the Surface Water Treatment Rule (40 CFR 141 Subpart H),
Interim Enhanced Surface Water Treatment Rule (40 CFR 141 Subpart P), Long-term 1 Enhanced Surface Water
Treatment Rule (40 CFR 141 Subpart P), and the Long-term 2 Enhanced Surface Water Treatment Rule (40 CFR 141
Subpart W).
3 Tier 2 and 3 notices are for violations and other situations that do not pose adverse health risks from short-term
exposure.
4 Source: U.S. EPA (2010) Revised Public Notification Handbook, EPA 816-R-09-013, March 2010.
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• Certain treatment technique violations under the suite of Surface Water Treatment Rules and
Ground Water Rule; or
• Occurrence of a waterborne disease outbreak or other waterborne emergency.
Although BWA policies vary by primacy agency, most follow these recommendations from the EPA. In
addition, primacy agencies' policies may also identify other situations that trigger BWAs.
As mentioned earlier, direct oversight of PWSs for compliance with NPDWRs is conducted through the
PWSS Program. Section 1413 of the SDWA gives states, territories and Tribes the opportunity to obtain
primacy for implementing the PWSS Program within their jurisdiction. To obtain and maintain primacy,
states, territories and Tribes must adopt and enforce drinking water standards that are at least as
stringent as the EPA's national standards (or the NPDWRs).
Primacy agencies' responsibilities related to drinking water standards include requiring that PWSs
monitor for contaminants, reviewing plans and specifications for PWS improvements, conducting on-site
inspections and sanitary surveys, issuing violations, providing training and technical assistance and
ensuring that PWSs inform their consumers about violations the PWS has incurred and the quality of the
water they are providing. Using annual Congressional appropriations under SDWA section 1413, the EPA
provides grants to eligible primacy agencies to develop and implement the PWSS Program. This funding
helps ensure the SDWA requirements are enforced and PWSs comply with the NPDWRs.
With the exceptions of Wyoming and the District of Columbia, all states, the Navajo Nation, and five U.S.
territories (i.e., Puerto Rico, the U.S. Virgin Islands, American Samoa, Guam, and the Commonwealth of
Northern Mariana Islands) currently have primacy for the NPDWRs. In cases where states, territories or
federally recognized Tribes do not assume primacy, the EPA serves as the primacy agency and
implements the PWSS Program directly. The EPA plays an important oversight role and retains its
independent compliance monitoring and enforcement authorities, even if a state, territory or Tribe has
primacy.
The EPA's authorities include Section 1414 of the SDWA, which provides the agency with the authority
to enforce violations of "any applicable requirement" of a state or federal program. Congress defined
"any applicable requirement" expansively to include, among other things, more stringent requirements
of a state primacy program. Section 1445 of the Act also provides the EPA with authority to request
information from a PWS or to conduct an onsite inspection of the system in order to determine
compliance or identify potential health risks. Finally, SDWA Section 1431 confers the EPA with
emergency authority to address contamination that "may present an imminent and substantial
endangerment to the health of persons." As noted above, the EPA may require a PWS to issue BWAs
and to take other related corrective measures, such as flushing the distribution of the system.
Data and Information Sources
The EPA used data available from a variety of sources to develop its analysis, each of which is described
below.
ASDWA and State Websites
The Association of State Drinking Water Administrators worked with the state drinking water programs
on their practices for tracking BWAs. Twenty (20) states responded with information. Some states
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responded that they planned to organize or begin tracking while other states indicated they do not have
plans to track BWA information.
The EPA also conducted searches on the state agencies websites using common terms such as "Boil
water/' "Boil Water Order (BWO)/BWA list," and "Public Notice Boil Water." Some BWA data were
obtained using targeted internet searches for state-specific datasets. The extent of information varied
from updated BWA databases with extensive information, including information for current BWAs and
lifted BWAs, to only current and on-going BWAs. In some cases, the BWAs are removed from the public
sites after the BWA has been lifted to avoid confusion for the public.
A few states had a section on their website dedicated to providing links to BWA notices, published by
local news outlets. Occasionally, links were inactive and inaccessible, or there was no indication of when
the BWA was lifted.
Online Searches
The Center for Accountability in Science (CAS)5 compiled a list of BWAs for calendar year 2021 that were
reported by news outlet articles. The CAS dataset includes information on the date reported, the
location affected, the number of people affected, the cause, the duration and the data source (news
article), if known. This list was developed by CAS through targeted internet searches; therefore,
additional searches for specific news articles reporting on BWAs were not conducted. The EPA
conducted further online research to verify that online database sources were captured to the extent
possible. The EPA also conducted general Google searches using common terms such as "Boil water,"
"Boil Water Order (BWO)/BWA list," and "Public Notice Boil Water" and a specific state, in the event the
state health and environmental agency site did not have an available BWA database.
SDWIS/Fed Data
The Safe Drinking Water Information System Federal Reporting Services is the EPA's national database
that manages and collects PWS information from primacy agencies, including reports of drinking water
standard violations, reporting and monitoring violations, and other basic information, such as water
system location, type and population served. In addition to using available information in SDWIS/Fed on
BWAs, the EPA also used the database to identify additional information about the BWAs identified
through the state information and online searches discussed above. For example, if a BWA included the
PWS name and/or PWS identification number (PWSID), that information was used to identify additional
information such as the primary water source (i.e., ground water vs. surface water) and PWS type (i.e.,
CWS, NTNCWS, TNCWS) for the BWA. For those BWAs that had limited information, including no official
PWS name or the PWSID, the water source and PWS type would be recorded as unknown.
Data Limitations to Identifying BWAs
The information compiled in this report was limited due to a variety of factors, including availability of
BWA data from primacy agencies, various data collection methodologies used by primacy agencies and
the different level of content provided in the BWAs.
5 Source: https://accountablescience.com/about-us/
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In most circumstances, primacy agencies are typically responsible for oversight of the issuance of BWAs.
While primacy agencies may require BWAs and BWA reporting, not all primacy agencies maintain
databases that track BWA occurrence and causes, and if they do, this tracking information is not always
publicly available. BWA information is managed using a variety of primacy agency-specific databases;
therefore, information regarding the issuance and causes of BWAs is also inconsistent in scope and
completeness. Primacy agencies' BWA tracking databases may have limited data fields and descriptions.
Some databases provided limited information on the BWAs, such as the name of the PWS, the general
reason for the BWA (e.g., microbial), and the start and end dates. Other datasets provided information
on whether the BWA event was caused by a specific natural disaster event, or attributed to scheduled
repairs in precautionary situations, as compared to a response to unpredictable events such as a main
break.
Some primacy agency databases for tracking BWAs indicate whether a violation also occurred during the
BWA event but may not fully describe the violation.
In general, the primacy agency BWA databases contained more BWA event information than was often
available in press releases to consumers. In a few instances, BWAs obtained for this study from press
releases did not contain details about the situations or causes prompting the BWAs. In some situations,
press releases contained geographic descriptions such as town names without including the PWS name;
therefore, the PWS type, size, and source were left as unknown [7.5 percent (302) of issued BWAs],
The EPA found other discrepancies in the data provided regarding the length of the BWAs. Numerous
BWAs appear to remain unresolved (i.e., no end date was provided), and it is unclear whether the end
date was simply not included in the dataset or if the situation remains unresolved. Out of all the BWAs
identified, 29.5 percent (1,190) appear to be open at the end of 2021 with six percent (241) remaining
open because the event was not documented as resolved. The status of the remaining 22.3 percent
(899) of the BWAs could not be determined.
The occurrence of unprotected cross-connections was not tracked in any BWA database. For this reason,
the occurrence of potential backflow contamination events could not be quantified.
Data Analysis
Reasons for Issuing BWAs
There are a variety of ways that water can be contaminated with microbial pathogens. The EPA analyzed
information collected on the BWAs issued across the United States to identify the most prevalent cause
of BWAs and any trends in PWS type, size, and source. The BWA events found in the data reviewed were
assigned to one of six categories. These categories are based on the highest level of known public risk in
decreasing order in terms of an identified or attributed public health risk. The six categories were:
• Category 1 - Microbial violation, microbial contamination identified, sanitary risks found,
treatment technique failures, and treatment interruptions.
• Category 2 - Long-term/extended deficiencies (vulnerable or improperly constructed source,
required treatment not provided).
• Category 3 - Natural or other disasters.
• Category 4 - Backflow events.
• Category 5 - Main breaks, distribution system repairs, and loss of water pressure events.
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• Category 6 - Unknown/not identified.
A detailed description of each category follows.
Figure 2 in the following section provides information on the number BWAs issued as a result of the
reason.
Category 1. Microbial violation, microbial contamination identified, sanitary risks found, treatment
technique failures, and treatment interruptions.
When a PWS incurs a microbially related health-based violation, or fecal contamination is identified at a
PWS, a BWA is typically issued in conjunction with required regulatory notices under 40 CFR 141 Subpart
Qto the public about the violation orfecal contamination. Records for health-based violations of this
nature are maintained by the primacy agency and include compliance schedules and enforcement
actions. These BWAs are usually directed by the primacy agency, or in some instances by the EPA in its
oversight role and are not precautionary in nature. They represent known situations when a PWS has
failed to meet microbial standards of the NPDWRs, has identified fecal contamination, or has failed to
provide required treatment. A few examples of these types of situations include:
• Fecal contamination or E. coli identified in the distribution system (microbial violation and/or
fecal contamination identified); and
• Failure to operate disinfection or filtration treatment as required (treatment technique failure).
In situations where coliform bacteria are found in the distribution system pipes of a water system, but
no NPDWR violation has occurred or fecal contamination is suspected but has not yet been confirmed,
there may still be the possibility of fecal contamination in the water system. This situation typically
involves issuing a precautionary BWA while additional sampling is performed to clarify whether fecal
contamination, measured as E. coli bacteria, is present. Additional situations in this category include:
• Interruptions in treatment where no violation was incurred; and
• The primacy agency has identified sanitary risks and the water system is in the process of
completing timely corrective action; however, there was no confirmed fecal contamination of
the water system.
Category 2. Long-/extended (vulnerable or improperly constructed source, required treatment not
provided)
This category of BWAs is associated with the quality of water sources and appropriate treatment of
those sources. If there is a change in water quality that indicates new microbial contamination at the
source, or if the source is ground water that is newly designated as being groundwater under the direct
influence of surface water (i.e., GWUDI) and as a result, vulnerable to microbial contamination and
additional treatment requirements may become necessary and an interim BWA may be issued. In
situations like these, the duration of BWAs may typically be longer than other BWAs where the cause
can be resolved without capital improvements due to the time needed to design the treatment system,
obtain related plan approvals and install the new treatment.
Similarly, structural changes may need to be made at the water system if the primacy agency finds
improperly constructed wells or intakes. These changes would also need time for design, permit
approval, and equipment modifications or installation.
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Category 3. Natural or other disasters
Natural or other disasters such as floods, ice storms, droughts, lightning storms and fires can cause
disruptions in water services. These include water main breaks, power outages, treatment or storage
failures and changes in source water availability. Although many PWSs assess vulnerabilities to improve
their resilience and capability to respond to adverse events, natural disasters can still damage PWSs
when infrastructure is overwhelmed by severe events. Quick restoration of service following a natural or
other disaster is important for providing quality water to consumers. The BWAs are often issued after
the storm when it becomes known that the PWS is adversely affected by the storm; however, a primacy
agency may require the PWS to issue a precautionary BWA in advance of an impending natural disaster
(e.g., hurricane).
Category 4. Backflow events
Normally, the operating pressure of a PWS drinking water distribution system prevents water in a
building's plumbing system from re-entering the PWS distribution system (i.e., backflow event). During a
backflow event, a loss of pressure in the distribution system or a higher pressure in the building
plumbing system can reverse the flow of water. If there is a connection between the PWS distribution
system and a building's plumbing system where a potential contaminant may be present that is not
protected by the appropriate method or backflow prevention device, this reversal of flow could cause
contamination of the drinking water supply.
Primacy agencies perform sanitary surveys to ensure water systems implement a cross-connection
oversight program. The EPA, either in a direct implementation role or an oversight role in a primacy
state, may conduct onsite evaluations by doing sanitary surveys or inspections and observe potential
cross connections. When an unprotected cross-connection is identified at a PWS, the PWS may be
required to issue a BWA until the cross-connection is protected or eliminated. For the issued BWAs of
this reporting period, there was no identified occurrence of an actual backflow contamination event that
resulted in a BWA being issued.
Category 5. Main breaks, distribution system repairs, and loss of water pressure events
Main breaks, distribution systems repairs, and loss of water pressure events can compromise the
protection provided in a public water supplier's distribution system and can result in microbial
contamination of the water supply. The water supply or pipes can be exposed to the soil or flooding of
streets while losses of system pressure can result in infiltration, reversed flows or siphon conditions that
can introduce water of unknown quality from customer's connections.
Main breaks can occur due to deteriorated infrastructure that is used beyond its expected service life,
seasonal freeze-thaw thermal expansion, localized pipe corrosion, or accidental rupturing of a water
main when other work is performed in the area, among other reasons. Deterioration of a water system's
distribution system infrastructure is a function of both material age and the cumulative effect of
hydraulic and operating forces acting on it. Main breaks and distribution system repairs can include
water main or valve leaks and service connection piping leaks.
Pressure management is an important element of water quality management for PWSs because it helps
to sustain high water quality and reduce water losses and main breaks. To maintain optimal water
pressure throughout the distribution system, the water system needs to address varying terrain
elevation and consumer water demand. System design or inadequate operating practices can contribute
to ineffective low and high pressures.
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The federal drinking water regulations consider maintaining continued positive water pressure in all
parts of the distribution system to be an operational practice that can achieve compliance with the
MCLs for E. coli
[40 CFR 141.631(3)]. Water systems must also meet any state water pressure requirements or local
plumbing codes.6
Loss of system pressure at a ground water source can commonly be attributed to well pump
malfunctions due to lack of power or insufficient source water quantity to meet system supply demands.
Other losses of system pressure in the distribution system that are not attributed to a main break can be
from power outages or from the storage facility, which may be impacted by leaks or planned activities
such as storage facility cleaning or inspection. 16.6 percent of the total BWA occurrences (668) were
attributed to power outages or other loss of system pressure unrelated to natural disaster events.
Power or pressure issues at the water source, unrelated to natural disaster events, were less than one
percent (33) of the total BWAs occurrences. Other losses of water pressure unrelated to natural disaster
events that were not attributable to source issues or main breaks were found to be 5.5 percent (222) of
the total BWA occurrences. 2.2 percent (88) of the total BWA occurrences were attributed to power
outages unrelated to weather events.
Category 6. Unknown/not identified.
Some of the primacy agency tracking methods do not specify the cause of the BWA event. This category
represents those BWAs for which information was not available to properly describe the BWA event.
BWAs by category
Figure 2 provides a breakdown of the various reasons for issuing a BWA with each reason described
earlier corresponding to a category. The largest reason identified for a PWS to issue a BWA is Category
5, main breaks and distribution system repairs and loss of water pressure events. Eighty percent of
BWAs (3,221) occurred due to main breaks, distribution system repairs and loss of water pressure
events. In the majority of water main break and repair situations, 63.2 percent of BWA events (2,550),
the primacy agency did not identify whether there was pressure loss impact. For those situations where
pressure loss was attributed to main breaks and distribution system repair situations, 12.5 percent of
BWA events (504) were reported to have resulted in uncontrolled loss of pressure, while 4.1 percent of
BWA events (167) were identified to have partial loss of pressure. Some distribution system repairs were
planned or scheduled distribution work and performed under a precautionary BWA. This analysis found
that 6.2 percent (252) of BWA events in all categories were attributed to planned or scheduled source,
treatment, or distribution system repairs.
The second highest category of an issued BWA was for unknown or unidentified reasons (Category 6) at
11.2 percent (454). Identified microbial contamination or events with the potential for fecal
contamination (Category 1) were a cause for 6.3 percent of the BWAs found (256). Natural or other
disasters (Category 3) were identified as a cause for 1.4 percent of BWAs found (57). There were no
backflows events found as a cause for BWAs.
6 Source: ASDWA (2020) State Drinking Water Distribution System Survey.
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Number of BWAs
1,500 2,000
2,500
3,000
3,500
3,221(79.8%)
Category 1: Microbial violation, microbial
contamination identified, sanitary risks found,
treatment technique failures, and treatment
interruptions
Category 2: Long-term/extended deficiencies
(vulnerable or improperly constructed source, required
treatment not provided)
Category 3: Natural or other disasters
Category 4: Backflow events
Category 5: Main breaks, distribution system repairs,
and loss of water pressure events
Category 6: Unknown/not identified
Figure 2: Reasons for Issuing BWAs in 2021
BWAs by system size
PWSs are often categorized by the number of people served (population served) by the PWS due to the
differences in available resources, capital, personnel, and other unique challenges. PWSs serving 10,000
or fewer customers represent more than 92 percent of all CWSs, and nearly all the NCWSs.7
For the purposes of this report, PWSs were divided into five size categories:
Very small: <500
Small: 501-3,300
Medium: 3,301 -10,000
Large: 10,001 -100,000
Very large: >100,000
As seen in Figure 3, 23.8 percent (961) of the BWAs were issued by large PWSs, while 22 percent (889)
were issued by small PWSs, and 19.9 percent (803) were issued by very small PWSs. When focusing on
PWSs serving less than 10,000 people, the BWAs for these size systems account for 58.1 percent (2,345)
of all issued BWAs in 2021. The system size could not be determined from the data collected for 10.5
percent (425) occurrences and are categorized and included as "unknown" in Figure 3.
7 Source: U.S. EPA (2011) National Characteristics of Drinking Water Systems Serving Populations Under 10.000.
EPA 816-R-10-022, July 2011.
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1,200
961(23.8%)
±,uuu 889 (22.0%)
„ 803(19.9%)
< 800
653(16.2%)
° 600
-Q
E
= 400
200
425(10.5%)
305 (7.6%)
I I
Very Small Small Medium Large Very Large Unknown
PWS Size
Figure 3: BWAs by PWS Size in 2021
For BWAs issued for Category 5 - main breaks, distribution system repairs, and loss of water pressure
events by PWS size - Figure 4 shows that 28.6 percent (921) of these issued BWAs were at large PWSs,
compared to the 24 percent for all issued BWAs (961), as shown in Figure 3. Meanwhile, the number of
very small PWSs that issued BWAs for main breaks, distribution system repairs and loss of water
pressure events is only 10.6 percent (341), compared to 20 percent for all issued BWAs (803).
1000 921(28.6%)
900
CO
< 800
£ 700
I" 600
CUD
S 500
-------
interruptions - were at very small PWSs. Similarly, 63.4 percent (288) of the Category 6 BWAs -
unknown/not identified - were at very small PWSs.
Category 1
Category 2
350
< 300
3
CO
^ 250
&, 200
a>
ro
150
O
100
E
3 50
350
^ 300
(N "U
8> 200
flj
if 150
0
Jj 100
1 50 39(81.3%)
2(4.2%) 0(0.0%) 1(2.1%) 1(2.1%) 5(10.4%)
111!
(43.4%)
30.5%)
/O 1,
40(15.6%)
¦ 13^1%) 14(5,5%) o(0o%)
r r i t i i i
Very Small Medium Large Very Unknown
Small Large
PWS Size
0 1 ^ 1 1 ! I 1 1
Very Small Medium Large Very Unknown
Small Large
PWS Size
Category 3
350
300
250
200
150
100
50 24(42.1%)
7(12.3%) 4(7.0%) 2(3.5%) 1(1.8%)
19 (33.3%)
Very Small Medium Large Very Unknown
Small Large
PWS Size
Category 5
921 (28.6%)
Very Small Medium Large Very Unknown
Small Large
PWS Size
Category 6
350
- 300 288 (63.4%)
61 (13.4%)
1
54 (11,9%)
24 (5.3%) 23 (5.1%)
4 (0.9%)
Very Unknown
Large
Small Medium Large
PWS Size
Figure 5: Reasons for Issuing BWAs by PWS Size in 2021
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BWAs by system type
Figure 6 shows a breakdown of the different PWS types (i.e., CWSs, NTNCWSs, and TNCWSs) and the
number of BWAs issued by each PWS type. The data shows that 80 percent of the BWAs issued (3,228)
were issued by CWSs while 7.1 percent (288) were issued by TNCWSs, three percent (122) were issued
by NTNCWSs, and 9.9 percent (398) of the BWAs were for unknown types of PWSs.
Figure 6: BWAs by PWS Type in 2021
For BWAs issued for Category 5 BWAs - main breaks and distribution system repairs by PWS type, Figure
7 shows that 88.9 percent of these issued BWAs (2,862) were at CWSs. NTNCWSs and TNCWSs each only
comprised approximately 1.9 percent (62) and 0.9 percent (28) of these BWAs, respectively, while 8.4
percent (269) of the PWS type was unknown.
1.9%
¦ CWS (2,862)
¦ NTNCWS (62) 1
0.9%
¦ TNCWS (28) I
ft ¦
8.4%
i Unknown (269)
Figure 7: BWAs under Category 5 - Main Breaks and Distribution System Repair - by PWS Type in 2021
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BWA by source type
PWSs are identified by their source type as either surface water PWSs or ground water PWSs. If a PWS
uses any surface water, it is identified as a surface water PWS even if they also use ground water. For
the BWA occurrences reviewed for this report, 31.8 percent (1,284) were by surface water source PWSs
while 57.7 percent (2,327) were PWSs served by a ground water source (Figure 8). The source water
type was unknown for 10.5 percent of the PWSs (425). When only looking at the BWAs issued for
Category 5 - main breaks, distribution system repairs, and loss of water pressure events - by PWS
source type, the percentages are about equal to all BWAs (i.e., 35.4 percent for systems served by a
surface water source (1,139), 56.3 percent for systems served by a ground water source (1,813), and 8.3
percent (269) for which the source type was unknown).
Figure 8: BWAs by PWS Source in 2021
Conclusion
PWSs are vital to the health, safety and economies of communities. Although consumers expect
continuous drinking water, a PWS may temporarily disrupt service or require consumers to take
precautionary measures to protect their health (e.g., boiling water before use). Such situations vary in
terms of scope, scale, severity, and cause.
SDWA primacy agencies or the EPA, either in its direct implementation role or in its oversight role, may
require BWAs and BWA reporting. BWA information is managed using a variety of primacy agency-
specific requirements and databases and is varied in scope and completeness across the country. The
EPA reviewed voluntary state submittal information on BWAs and publicly available data to understand
the occurrence and reasons for issuing a BWA across the United States.
Eighty percent (3,221) of the BWAs found for this report occurred due to main breaks, distribution
system repairs, and loss of water pressure events (Category 5 BWAs) and not necessarily associated with
violations of SDWA or the National Primary Drinking Water Regulations. Other contributing causes were
evidence of microbial contamination or treatment failure and natural disasters. The primary PWS source
(i.e., ground water vs. surface water) and the PWS size (i.e., population served) did not have much of an
18
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effect on the number of BWAs issued. However, the specific reasons for issuing a BWA varied by PWS
size. Very small water systems (serving less than 500) had the highest number of BWAs in categories 1,2,
3 and 6. This may reflect the continuing challenges faced by very small water systems in maintaining
compliance with the NPDWRs and adequate infrastructure due to the lack of technical, managerial and
financial capacities. This also may be reflected in the number of ground water systems with BWAs
compared to the number of surface water systems with BWAs. More than 90 percent of public water
systems serving less than 10,000 people use a groundwater source. More data on the BWAs and
information on why the BWAs were issued would support a more comprehensive and more nationally
representative analysis to fully capture and understand the prevalence and occurrence of BWAs.
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Appendices
Appendix A. Acronym List
ASDWA
BWA
BWO
CAS
CWS
EPA
GW
MCL
NCWS
NPDWR
NTNCWS
PWS
PWSID
PWSS
SDWA
SDWIS/Fed
SW
SWTR
TNCWS
Association of State Drinking Water Administrators
Boil Water Advisory
Boil Water Order
Center for Accountability in Science
Community Water System
U.S. Environmental Protection Agency
Ground Water
Maximum Contaminant Level
Non-Community Water System
National Primary Drinking Water Regulation
Non-Transient Non-Community Water System
Public Water System
Public Water System Identification Number
Public Water System Supervision
Safe Drinking Water Act
Safe Drinking Water Information System Federal Reporting Services
Surface Water
Surface Water Treatment Rule
Transient Non-Community Water System
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Appendix B. Example Boil Water Advisory
Below is an example of the EPA's BWAfor an E. coli maximum contaminant level (MCL) violation.
Revised Total Coliform Rule (RTCR) E. coli MCL Violation Notice - Template 1-2
DRINKING WATER WARNING
E. coli is present in [Water System Name]'s water
BOIL YOUR WATER BEFORE USING
[Briefly describe the situation, such as: coli bacteria were found in the water supply on [give date]" or "We did not
perform required testing of the water system and must assume that E. coli bacteria are in the water as of [give date]]. These
bacteria can make you sick, and are especially a concern for people with weakened immune systems.
Bacterial contamination can occur when increased run-off enters the drinking water source (for example, following heavy
rains). It can also happen due to a break in the distribution system (pipes) or a failure in the water treatment process.
What should 1 do? What does this mean?
DO NOT DRINK THE WATER WITHOUT BOILING IT FIRST. Bring all water to a boil, let it boil for one minute and let it
cool before using, or use bottled water. Boiled or bottled water should be used for drinking, making ice, brushing
teeth, washing dishes, and food preparation until further notice. Boiling kills bacteria and other organisms in the
water.
*E. coli are bacteria whose presence indicates that the water may be contaminated with h uman or animal wastes.
Human pathogens in these wastes can cause short-term effects, such as diarrhea, cramps, nausea, headaches, or
other symptoms. They may pose a greater health risk for infants, young children, the elderly, and people with
severe// compromised immune systems. *
The symptoms above are not caused only by organisms in drinking water. If you experience any of these symptoms
and they persist, you may want to seek medical advice. People at increased risk should seek advice from their
healthcare providers about drinking this water.
What is being done?
[Describe corrective action]. We will inform you when tests show no bacteria are present and you no longer need to boil your
water. We anticipate resolving the problem within [estimated timeframe].
For more information, please contact [name of contact] at [phone number] or [mailing address]. General guidelines on ways
to lessen the risk of infection by bacteria and other disease-causing organisms are available from the EPA Safe Drinking Water
Hotline at 1-800-426-4791.
*Please share this information with all the other people who drink this water, especially those who may not
have received this notice directly (for example, people in apartments, nursing homes, schools, and
businesses). You can do this by pasting this notice in a public place or distributing copies by hand or mail. *
This notice is being sent to you by [water system name]. State Water System ID#: .
Date distributed: .
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