United States
      Environmental Protection


Comprehensive Surface Water Treatment Rules
Quick Reference  Guide: Unfiltered Systems
 Overview o
             Surface Water Treatment Rule (SWTR) - 40 CFR 141 .70-141 .75
             Interim Enhanced Surface Water Treatment Rule (IESWTR) - 40 CFR 141 .170-141.175
             Long Term 1 Enhanced Surface Water Treatment Rule (LT1 ESWTR) - 40 CFR 1 41 .500-1 41 .571
             Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) - 40 CFR 1 41 .700-1 41 .722
             Improve public health protection through the control of microbial contaminants, particularly
             viruses, Giardia lambia, and Cryptosporidium.
             The Surface Water Treatment Rules:
             ^  Applies to all public water systems (PWSs) using surface water or ground water under the direct
                influence of surface water (GWUDI), otherwise known as "Subpart H systems."
             >  Requires all Subpart H systems to disinfect.
             >  Requires Subpart H systems to filter unless specific filter avoidance criteria are met.
             ^  Requires unfiltered systems to perform surface water monitoring and meet site specific conditions
                for controls of microbials.
                                  "This document provides a summary of federal drinking water requirements; to ensure full compliance, please consult
                                  the federal regulations at 40 CFR 141 and any approved state requirements.
                                  Overview of Requirements
                                  The purpose of this table is to show how the requirements for the IESWTR, LT1ESWTR and LT2ESWTR build
                                  on the existing requirements established in the original SWTR.
                                  APPLICABILITY: PWSs that use surface water or GWUDI
                                  (Subpart H systems) that do not provide filtration.
                                  Source Water
                                  Profiling and
                                  Surveys (state
                                  Water Storage
                                                             > 10,000
                                                             < 10,000
             99.99% (4-log) removal/inactivation of viruses
                                               99.9% (3-log) removal/inactivation of Giardia
             99% (2-log) removal of
             Cryptosporidium (through watershed control)
                                               99% (2-log) inactivation of Cryptosporidium
                                               for systems reporting < 0.01 oocysts/L;
                                               99.9% (3-log) inactivation of Cryptosporidium
                                               for systems reporting > 0.01 oocysts/L.
                                               Entrance to distribution system (a 0.2 mg/L)
             Detectable in the distribution system
                                               Must use a minimum of two disinfectants to
                                               meet the Cryptosporidium, Giardia lamblia,
                                               and virus inactivation requirements.
             Monitoring of Cryptosporidium to calculate
             arithmetic mean of sample concentrations and
             determine additional treatment requirements
             Avoidance Criteria
                                                                                                  Final Rule Dates
                                                          For sanitary
                                                         provisions only
under SWTR
                                                         under SWTR

under SWTR
            under SWTR
under SWTR
            under SWTR
                        IESWTR and
                        LT1 ESWTR
                                                         under SWTR
under SWTR
             Systems must profile inactivation levels and
             generate benchmark, if required
             CWS**: Every 3 years
             NCWS": Every 5 years
             All new facilities constructed must be covered
                                               Uncovered finished water facilities must be
                                               covered or discharge treated
                                   Operated by Qualified Personnel as Specified by State
            under SWTR
under SWTR
            under SWTR
under SWTR
                        under SWTR,
                        IESWTR and
                        LT1 ESWTR
                        IESWTR and
                        LT1 ESWTR
                                                         under SWTR
            under SWTR
            under SWTR
                                  "Community water system (CWS), Noncommunity water system (NCWS)

Filtration Avoidance Criteria
Since December 30, 1991, systems must meet source water quality and site specific conditions to remain unfiltered. If any of
the following criteria to avoid filtration are not met, systems must install filtration treatment within 18 months of the failure. The
following table outlines the avoidance criteria established by the SWTR and later enhanced by the IESWTR and LT1ESWTR.
 Filtration Avoidance Crite
 Water Quality
Monitor fecal coliform or total coliform density in representative
samples of source water immediately prior to the first point of
disinfection application:
^  Fecal coliform density concentrations must be & 20/100 ml;
>  Total coliform density concentrations must be < 100/100 ml.
Sample results must satisfy the criteria listed above in at least 90%
of the measurements from previous 6 months.
1 to 5 samples per week depending on system size, AND
Every day the turbitidy of the source water exceeds 1 NTU
           Prior to the first point of disinfection application, turbidity levels
           cannot exceed 5 NTU.
                                                         Performed on representative grab samples of source water
                                                         every 4 hours (or more frequently)	
           Calculate total inactivation ratio daily and provide 3-log Giardia
           lamblia and 4-log virus inactivation daily (except any one day each
           month) in 11 of 12 previous months (on an ongoing basis).
                                                         Take daily measurements before or at the first customer at
                                                         each residual disinfectant concentration sampling point:
                                                         ^ Temperature
                                                         > pH (if chlorine used)
                                                         > Disinfectant contact time (at peak hourly flow)
                                                         ^ Residual disinfectant concentration measurements (at
                                                           peak hourly flow)
 Site Specific
   MCL for total coliforms in 11 of 12 previous months (as per Total Coliform Rule)
   Stage 1 Disinfectants and Disinfection Byproducts Rule requirements.
              must have:
              Adequate entry point residual disinfectant concentration (see disinfection requirements).
              Detectable residual disinfectant concentration in the distribution system (see disinfection requirements).
              Redundant disinfection components or automatic shut-off whenever residual disinfectant concentration < 0.2 mg/L.
              A watershed control program minimizing potential for contamination by Giardia lamblia cysts and viruses in source water;
              IESWTR and LT1 ESWTR update this requirement by adding Crypotosporidium control measures.
              An annual on-site inspection by state or approved third party with reported findings.
              Not been identified as a source of a waterborne disease outbreak.
Disinfection must be sufficient to ensure that the total treatment process of the system achieves at least:
> 99.9% (3-log) inactivation and/or removal of Giardia lamblia.
> 99.99%  (4-log) inactivation and/or removal of viruses.
Subpart H systems  using chlorine dioxide, ozone, or ultraviolet (UV) disinfection must achieve additional Cryptosporidium log
credit by using the Microbial Toolbox option under the  LT2ESWTR. Systems must also comply with the maximum residual
disinfectant level (MRDL) and maximum contaminant levels (MCL) requirements specified in the Stage 1 Disinfectants and
Disinfection Byproducts Rule (Stage 1  DBPR) and the Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2  DBPR).
 Residual  Disinfectant Monitoring and  Reporting Requirements
                                                             Monitoring Frequency
                                                                              (Reports due 10th of the following month)
 Entry to distribution
     Residual disinfectant concentration cannot
     be < 0.2 mg/L for more than 4 hours.
                              Continuous, but states may allow
                              systems serving 3,300 or fewer
                              persons to take grab samples from
                              1 to 4 times per day, depending on
                              system size.	
  Lowest daily value for each day, the date and duration
  when residual disinfectant was < 0.2 mg/L, and when
  state was notified of events where residual disinfectant
  was < 0.2 mg/L.
 Distribution system -
 same location as
 total coliform sample
     Residual disinfectant concentration cannot
     be undetectable in greater than 5% of
     samples in a month, for any 2 consecutive
     months. Heterotrophic plate count (HPC)
      500/mL is deemed to have detectable
     residual disinfectant.
                              Same time as total coliform
  Number of residual disinfectant or HPC measurements
  taken in the month resulting in no more than 5% of
  the measurements as being undetectable in any 2
  consecutive months.

LT2ESWTR Source Water Monitoring and Treatment Requirements
Each PWS must determine the arithmetic mean of all Cryptosporidium samples collected during monitoring.
A combined distribution system (CDS) is an interconnected distribution system consisting of the distribution systems of the
wholesale system and of the consecutive systems that receive finished water from that wholesale system.  Under the LT2ESWTR,
wholesale systems in a CDS must comply with the LT2ESWTR based on the population of the largest system in their CDS.
EPA has established four schedule categories based on system size to simplify the discussion of the LT2ESWTR monitoring
requirements. Schedule 1 applies to systems that serve 100,000 or more people or in a CDS that largest system serves 100,000
people.  Schedule  2 applies to systems that serve 50,000 to 99,999 people or in a CDS that largest system serves 50,000 to
99,999 people. Schedule 3 applies to systems that serve 10,000 and 49,999 people or in a CDS that largest system serves
10,000 and 49,999 people. Schedule 4 applies to systems that serve less than 10,000 people.

Source water monitoring requirements are as follows:
>  Schedule 1-3 systems must sample for Cryptosporidium at least monthly for 2 years.
>  Schedule 4 systems must sample for Cryptosporidium at a frequency of either (a)  at least 2 times per month for 1 year or (b) 1
   time per month for 2 years.
>  All systems must begin a second round of monitoring no later than 6 years after determining initial Cryptosporidium level.
  If Arithmetic Mean Cryptosporidium
             Level is:
 System Must Provide Treatment
             Disinfectant System Must Use:
 < 0.01 oocysts/L
2-log Cryptosporidium inactivation
 > 0.01 oocysts/L or if PWS chooses not
 to monitor for Cryptosporidium
3-log Cryptosporidium inactivation
At least 2 disinfectants to provide 4-log virus, 3-log Giardia lambia and
2- or 3-log Cryptosporidium inactivation.
Each disinfectant must achieve by itself the total inactivation required
for one of these target pathogens
* Inactivation credit for treatment with chlorine dioxide, ozone or UV light.

Microbial Toolbox: Inactivation Options, Credits and Criteria
The Microbial Toolbox provides a list of the tools that systems can use, and receive treatment credits for, in order to meet
additional treatment requirements of LT2ESWTR. The toolbox provides systems with the flexibility to use any combination of
applicable treatment options as long as the systems are in compliance with design, operational, and performance criteria which
are not detailed in this document. Unfiltered systems must use one of the following inactivation/disinfection tools to receive the
corresponding credits:
>  Chlorine dioxide: log credit received is based on measured CT in relation to the CT table.
>  Ozone: log credit received is based on measured CT in relation to the CT table.
>  UV: log credit received is based on validated UV dose in relation to the UV dose table; reactor validation testing is required to
   establish UV dose and associated operating conditions.

System Reporting Requirements
System Reporting Requirements
Report to State:
Within 1 0 days after the end of
the month:
Within 10 days after the end
of the first month following the
month when the source water
monitoring sample(s) were
By October 1 0 each year:
Within 24 hours:
ASAP but no later than the end
of the next business day:
Based on system's LT2ESWTR
What to Report:
^ Source water quality information (microbial quality and turbidity measurements).
> In addition to the disinfection information above, systems must report the daily residual disinfectant concentration(s) and
disinfectant contact time(s) used for calculating the CT value(s).
> Results from the required source water monitoring.
^ Report compliance with all watershed control program requirements.
^ Submit report on the on-site inspection, unless that state conducted the inspection, in which case the state must provide the
system with a copy of the report.
> Turbidity exceedances of 5 NTU and waterborne disease outbreaks.
> Instance where the residual disinfectant level entering the distribution system was < 0.2mg/L
> Sampling schedules and monitoring results for source water monitoring
^ Certain data elements of Cryptosporidium, E. coli and turbidity analyses.
*See each of the four LT2ESWTR by schedule QRGs available online at http://water.epa.gov/lawsregs/rulesregs/sdwa/lt2/compliance.cfm for additional details.

Disinfection Profiling and Benchmarking Requirements
A disinfection profile is the graphical representation of a system's microbial inactivation over 12 consecutive months.
A disinfection benchmark is the lowest monthly average microbial inactivation value. The disinfection benchmark is used as a
baseline of inactivation when considering changes in the disinfection process.
 Disinfection Profiling and  Benchmarking Requirements
 The purpose of disinfection profiling and benchmarking is to allow systems and states to assess whether a change in disinfection practices reduces
 microbial protection. Systems must develop a disinfection profile that reflects Giardia lamblia and viruses inactivation, calculate a benchmark
 (lowest monthly inactivation) based on the profile, and consult with the state prior to making a significant change to disinfection practices.
Community water systems (CWS),
nontransient noncommunity water systems
(NTNCWS), and transient noncommunity
water systems (TNCWS) serving >10,000.
CWS and NTNCWS serving
<10,000 only.
Any CWS, NTNCWS, or TNCWS that proposes to
make a significant change in disinfection practice*.
 Profiling By:
April 1, 2000
   July 1, 2003, for systems
   serving 500-9,999 people.
   January 1, 2004, for systems
   serving < 500 people.
   Upon completion of initial round of source water
   monitoring, AND
   12 consecutive months prior to making the
   proposed change.
 Frequency &
Daily monitoring for 12 consecutive calendar
months to determine the total logs of Giardia
lamblia inactivation (and viruses, if necessary)
for each day in operation.
Weekly inactivation of Giardia
lamblia (and viruses, if necessary),
on the same calendar day each
week over 12 consecutive months.
At least weekly inactivation of Giardia lamblia and
viruses, for at least 1 year. May use data collected for
profile under IESWTR and LT1SWTR.
 May Waive
TTHM annual average <0.064 mg/L and HAAS
annual average <0.048 mg/L:
^  Collected during the same period.
>  Annual average is arithmetic average of
   the quarterly averages of 4 consecutive
   quarters of monitoring.
^  At least 25% of samples at the maximum
   residence time in the distribution system.
>  Remaining  75% of samples at
   representative locations in the distribution
One TTHM sample <0.064 mg/L
and one HAAS sample <0.048
>  Collected during the month of
   warmest water temperature;
^  At the maximum residence time
   in the distribution system.
Samples must have been collected
after January 1, 1998.
   The system has an existing disinfection profile for
   both Giardia lamblia and viruses, and has neither
   made a change in disinfection practices nor
   changed sources since the profile was developed;
   The system has at least 1 year of existing data
   that can be used to complete a disinfection profile,
   and has neither made a significant change to its
   treatment practice nor changed sources since the
   data were collected.
 Must be
 Calculated If:
   Systems required to develop a disinfection
   profile and are considering making
   a significant changes in disinfection
   Systems must consult the state prior to
   making any modifications to disinfection
Same as IESWTR, and systems
must obtain state approval prior
to making any modifications to
disinfection practices.
Complete a disinfection profile and benchmark for
viruses and Giardia lamblia.
*A significant change in disinfection practice is defined as (1) change in the point of disinfection, (2) change to the type of disinfectant, (3) change to the disinfection
process, or (4) any other modification designated by the state.
      Office of Water (4606M)
                           EPA 816-B-10-001
                            August 2010