&EPA
United States
Environmental Protection
Agency
Online Water Quality Monitoring Primer
For Water Quality Surveillance and Response Systems
Office of Water (MC 140)
EPA817-B-15-002A
May 2015
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Introduction
A Water Quality Surveillance and Response System (SRS) provides a systematic framework for
enhancing distribution system monitoring activities to detect emerging water quality issues and respond
before they become problems. An SRS consists of six components grouped into two operational phases,
surveillance and response. The surveillance components are designed to provide timely detection of
water quality incidents in drinking water distribution systems and include: Online Water Quality
Monitoring, Enhanced Security Monitoring, Customer Complaint Surveillance and Public Health
Surveillance. The response components include Consequence Management and Sampling & Analysis,
which support timely response actions that minimize the consequences of a contamination incident. The
Water Quality Surveillance and Response System Primer provides a brief overview of the entire system
(USEPA, 2015).
This document provides an overview of Online Water Quality Monitoring
(OWQM), a surveillance component of an SRS. It presents basic information
about the goals and objectives of OWQM in the context of an SRS. This
primer covers the following four topics:
• Topic 1: What is OWQM?
• Topic 2: What are the major design elements of OWQM?
• Topic 3: What are common design goals and performance objectives
for OWQM?
• Topic 4: What are cost-effective approaches for OWQM?
Topic 1: What is OWQM?
OWQM utilizes real-time water quality data collected from monitoring stations deployed at strategic
locations in a distribution system. The data generated at these stations is continuously analyzed to
support system operation and detect water quality anomalies.
OWQM provides valuable insight into real-time conditions throughout a distribution system. This
information allows utilities to detect incidents of unusual water quality which can allow for earlier, and
thus more effective, corrective actions if necessary. It can also be used to derive day-to-day benefits, such
as optimizing system operation, supporting regulatory compliance and enhancing asset management.
Benefits derived from OWQM are further described under Topic 3 of this document.
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Topic 2: What are the major design elements of OWQM?
The major design elements associated with OWQM are summarized in Figure 1 and described under the
remainder of this topic.
Data Generation
Monitoring stations
continuously measure water
quality parameters at
strategically identified
locations in a distribution
system
Figure 1. OWQM Design Elements
Data Communication
Data is transmitted to a
central location
Information Management &
Analysis
Information is made available to
utility staff, and data is analyzed to
identify water quality anomalies
Alert Investigation
Utility staff are alerted to
anomalies and initiate an
investigation
Data Generation
The data generation design element determines the water quality data produced through OWQM. It is
defined by the following three decisions:
• What to monitor: The parameters monitored in distribution systems determine both the
information available to utility staff and the types of water quality incidents that can be detected
by OWQM. Monitoring can include:
o Conventional parameters such as, disinfectant residual,
pH, turbidity, specific conductance, oxidation-reduction
potential and temperature
o Advanced parameters such as, TOC and UV-Vis spectral
absorbance
o Hydraulic parameters such as, pressure and flow
DID You KNOW?
Many drinking water
utilities have existing
capabilities and resources
that can provide the
foundation for OWQM.
• How to monitor: The sensor technologies used to monitor selected parameter(s), as well as the
equipment required to install this technology at monitoring stations, can dramatically impact the
capital costs, operating costs, data accuracy and required maintenance associated with OWQM.
• Where to monitor: Monitoring stations can be located anywhere in a distribution system, and
may include utility-owned facilities (pump stations and storage tanks), city-owned facilities (fire
and police stations), large water users such as bottling plants and hotels, and stand-alone
installations.
Data Communication
The data communication design element involves the transmission of OWQM data to a central location
for storage and access. Methods of communication for OWQM may include digital subscriber lines,
cellular networks, radio and city-owned wireless networks. The type and quantity of data produced,
existing communication capabilities and the locations from which data must be transmitted can impact
selection of data communication solution(s).
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Information Management and Analysis
Information Management: An information management system receives information, processes and
stores it, and makes it available to users. Below are sample screen shots of user interfaces through which
users can access, view and manipulate OWQM information. Figure 2 shows a screen developed within a
SCADA system to display recent values of all parameters measured at a given monitoring location.
Figure 3 shows a sophisticated, GIS-based interface in which the status of all monitoring stations can be
viewed at a glance. In both cases, users can navigate within the interface to get more details about
parameter values, alerts and station status.
Station 3 Trend Summary (USF/GE)
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Figure 4. Example of a Water Quality Anomaly
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Alert Investigation
When an alert is received, utility personnel follow defined alert investigation procedures to identify its
cause. In many cases, a simple review of information is sufficient to determine that an alert does not
indicate anomalous water quality, and is therefore invalid. Common causes of invalid alerts include
sensor malfunction and data communication failure. If a cause can't be identified through data review, an
on-site investigation can be conducted at the monitoring location that generated the alert to determine if
accurate data is being generated and communicated. A sample may be collected at the site to further aid
the investigation.
If it is determined that an alert was caused by a water quality incident, it may be necessary to take
corrective actions to mitigate potential consequences. For example, if the alert was caused by low
disinfectant residual data, steps may be taken to increase concentrations in the area. However, if a cause
cannot be determined, the possibility of system contamination is further investigated using procedures in
the utility's consequence management plan.
Topic 3: What are common design goals and performance objectives
for OWQM?
The design goals and performance objectives established for OWQM by a utility provide the basis for the
design of an effective component.
OWQM Design Goals
Design goals are the specific benefits that utilities expect to achieve by implementing OWQM. A
fundamental design goal of an SRS is the ability to detect and respond to water quality incidents in a
distribution system. In addition to this fundamental SRS design goal, other OWQM-specific design
goals, such as optimizing water quality in the distribution system, can be realized. Examples of common
OWQM design goals are listed in Table 1.
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Table 1. Examples of Common OWQM Design Goals
Design Goal
Detect water quality incidents
Optimize system operation
Support compliance with water
quality goals and regulations
Enhance asset management
Description
OWQM data can be used to detect unusual water quality conditions in
distribution systems. This can include regular system occurrences such as
nitrification, pressure transients, rusty or turbid water, treatment process failures,
pipe breaks and excessive water age. OWQM also provides the ability to detect
foreign substances in distribution systems resulting from leaky pipes, inadvertent
cross-connections, backflow events, chemical overfeeds during treatment and
intentional contamination.
Knowledge of real-time water quality and improved understanding of the impact
of operational changes on water quality and hydraulic flow paths may allow staff
to better manage application of treatment chemicals and may inform pump, valve
and tank operation.
Information collected throughout a distribution system, particularly in areas of
concern, can help identify when water quality goals aren't met and can provide
time for corrective action in order to avoid potential compliance issues.
Regular data review can reveal changes in system conditions that can affect the
performance and longevity of assets such as pipes, pumps, valves and storage
tanks.
OWQM Performance Objectives
Performance objectives are measurable indicators of how well an SRS meets the design goals established
by a utility. Throughout design, implementation and operation of an SRS or its components, utilities can
use performance objectives to evaluate the added value of each capability, procedure or partnership.
While specific performance objectives should be developed by each utility in the context of its unique
design goals, general performance objectives for an SRS were defined in the Water Quality Surveillance
and Response System Primer (USEPA, 2015) and are further described in the context of OWQM as
follows.
• Incident coverage: Maximize the types of water quality incidents that can be detected. The
types of water quality changes that can be detected by a specific OWQM component are
determined by the parameters monitored, as an incident can only be detected if it causes a change
in a monitored parameter.
• Spatial coverage: Maximize the portion of a distribution system that is monitored. For OWQM,
this is determined by the number and locations of monitoring stations, as incidents of abnormal
water quality can only be detected if affected water flows through a monitoring station.
• Timeliness of detection: Minimize the time required to detect a water quality anomaly. For
OWQM, detection time includes the time for the unusual water to flow to a monitoring location,
the time for an alert to be generated based on this data, and the time for utility staff to recognize
the alert and complete alert investigation procedures.
• Operational reliability: Maximize the percentage of time that OWQM is fully operational. This
requires proper maintenance of all equipment and information management systems, as well as
consistent implementation of standard operating procedures by utility personnel.
• Alert occurrence: Minimize the number of invalid alerts, which are not caused by abnormal
water quality, while maintaining the ability of the system to detect true water quality anomalies.
Alerting is primarily impacted by the accuracy of OWQM data generated and the data analysis
method(s) used.
• Sustainability: Realize benefits that justify the costs and level of effort required to implement
and operate OWQM. Benefits are largely determined by the information produced by the system,
which allows for day-to-day system monitoring and detection of water quality incidents. Costs
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include the capital and ongoing costs and level of effort required to implement and operate the
equipment and systems, as well as the effort required to investigate alerts generated.
Topic 4: What are cost-effective approaches for OWQM?
Utilities can take the following simple steps to develop the foundation for OWQM:
• Utilize distribution system water quality data already being collected (for example, disinfectant
residual concentrations at utility-owned facilities).
• Build SCADA screens that display data plots or develop spreadsheets for data review.
• Establish procedures for regular, manual review of data (for example, reviewing data at the
beginning of each shift) or create parameter setpoint alerts.
• Establish procedures for investigating water quality anomalies and train staff on their execution.
Next Steps
Visit the Water Quality Surveillance and Response Website at http://water.epa.gov/infrastructure
/watersecuritv/lawsregs/initiative.cfm for more information about SRS practices. The Website contains
guidance and tools that will help a utility to enhance surveillance and response capabilities, as well as
case studies that share utility experiences with SRS implementation and operation.
References
USEPA. (2015). Water Quality Surveillance and Response System Primer, 817-B-15-002.
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