ISO/TS 24541:2020
(Main)Service activities relating to drinking water supply, wastewater and stormwater systems — Guidelines for the implementation of continuous monitoring systems for drinking water quality and operational parameters in drinking water distribution networks
Service activities relating to drinking water supply, wastewater and stormwater systems — Guidelines for the implementation of continuous monitoring systems for drinking water quality and operational parameters in drinking water distribution networks
This document specifies guidelines for the implementation of continuous monitoring systems for drinking water quality and operational parameters in drinking water distribution networks. It provides guidance for determining the: — effective number of continuous monitoring stations in the drinking water distribution network; — location of monitoring stations in the drinking water distribution network; — types of operational and drinking water quality parameter measuring devices (MDs) that can be installed in a continuous monitoring station; — quality control, maintenance and calibration requirements of the continuous monitoring system. This document excludes guidance on the design, structure, number and type of MDs to be installed in a continuous monitoring system.
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TECHNICAL ISO/TS
SPECIFICATION 24541
First edition
2020-11
Service activities relating to drinking
water supply, wastewater and
stormwater systems — Guidelines for
the implementation of continuous
monitoring systems for drinking water
quality and operational parameters in
drinking water distribution networks
Reference number
©
ISO 2020
© ISO 2020
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ii © ISO 2020 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principles . 6
5 Considerations for the justification of need for continuous monitoring .7
5.1 General . 7
5.2 Cost-benefit . 7
5.3 Risks of continuous monitoring . 8
5.4 Local contexts . 9
6 Choosing parameters to be monitored . 9
7 Locating the continuous monitoring stations in the drinking water distribution
network .12
7.1 General .12
7.1.1 Network layout .12
7.1.2 Development or implementation of an existing hydraulic or statistical
model of the drinking water distribution network (preferred) .12
7.1.3 The pragmatic approach .12
7.2 Locations for monitoring stations .13
7.2.1 General.13
7.2.2 The pragmatic approach .13
7.2.3 The hydraulic model approach .14
7.3 Network alert definition .14
7.4 Decision support tools .14
7.5 Periodic evaluation of the continuous monitoring system .14
8 Installation, maintenance, operation, calibration and data transmission of MDs .14
8.1 Installation considerations .14
8.1.1 General.14
8.1.2 Geographical location .15
8.1.3 Site installation location .15
8.2 Maintenance and operational considerations .15
8.3 Calibration considerations .16
8.4 Communication considerations .16
Annex A (informative) Examples of positives and negatives of continuous monitoring systems .17
Annex B (informative) Examples of commonly deployed drinking water quality parameter
measuring devices .19
Annex C (informative) Evaluation of the performance of measuring devices .23
Bibliography .24
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 224, Service activities relating to drinking
water supply, wastewater and stormwater systems.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved
Introduction
Cases of drinking water contamination around the world have raised awareness of water utilities'
exposure to risk. Contamination can arise from many causes, including societal mishaps, errors in
operation, maintenance or management by the water utility, natural disasters, vandalism, sabotage,
criminality and terrorist activity. The distributed nature of drinking water systems makes them
especially vulnerable to contamination and can permit the rapid dispersion of a contaminant. The
velocities and volumes of water in a drinking water distribution network can result in contamination
affecting significant numbers of users in a short time (e.g. tens of minutes). Recognition of these risks
has raised awareness of the need to consider the use of continuous monitoring systems to rapidly detect
potential contamination events.
The occurrence of an event can rarely be predicted. However, the more frequently relevant data can
be collected and examined, the greater is the chance of quickly detecting an event's occurrence. This
supports consideration of the adoption of continuous monitoring systems to provide the data streams
that can be used in event detection.
A contamination event can make a waterworks or a drinking water distribution network unusable for a
time and require implementation of contingency plans. Such plans could involve, for example, accessing
an alternative source water or providing an alternative water service other than via the drinking water
distribution network.
To date, very few water utilities have installed continuous monitoring systems either in part or
throughout their drinking water distribution network(s). This situation can result from a rational
decision based on risk assessment and, in some cases, a cost-benefit analysis. However, it should be
acknowledged that circumstances can change – gradually over time or rapidly in the face of events.
Water utilities wishing to explore such an option can face uncertainties and gaps in their knowledge on
how to proceed. In such circumstances water utilities typically face three main challenges:
— which types of measuring devices (MDs) to install in each continuous monitoring station;
— how many continuous monitoring stations to install per drinking water system;
— where to locate the continuous monitoring stations in the drinking water distribution network in
order to achieve the best results.
The installation of continuous monitoring systems could reduce the risk to public health and mitigate
the impact on users and other stakeholders during a contamination event. The value of continuous
monitoring systems can be determined using appropriate risk assessment and cost-benefit analysis.
Such an evaluation should take into account existing controls and establish the additional risk
mitigation that might be achieved and likely costs.
Advances in MD technology have recently made the adoption and deployment of continuous monitoring
more practicable. MDs are not limited to the measurement of drinking water quality alone. Continuous
measurement of operational parameters such as water flow and water pressure can improve the water
utility's capability to interpret results from the measurement of drinking water quality.
This document provides water utilities, their contractors, consultants and regulators with guidelines
for the installation of continuous monitoring systems in drinking water systems, including guidance on
their appropriate selection, maintenance and optimal calibration.
These guidelines can aid a water utility's processes for risk assessment and cost-benefit analysis. Taken
together these can help a water utility's top management take informed, risk-based decisions on the
worthwhileness of investment in a continuous monitoring system.
The guidance provided in this document is intended to be universally applicable, regardless of the
structure and size of a water utility's drinking water system. An event detection process (EDP) that
relies upon grab samples and intermittent data inputs could be implemented at lower cost. However,
where a water utility's assets, finances, management system and technical capability make it
practicable, the ability to provide continuous data streams offers advantages for event detection.
To gain experience, initial deployment could be limited to higher-risk areas within a wider drinking
water system.
vi © ISO 2020 – All rights reserved
TECHNICAL SPECIFICATION ISO/TS 24541:2020(E)
Service activities relating to drinking water supply,
wastewater and stormwater systems — Guidelines for
the implementation of continuous monitoring systems
for drinking water quality and operational parameters in
drinking water distribution networks
1 Scope
This document specifies guidelines for the implementation of continuous monitoring systems for
drinking water quality and operational parameters in drinking water distribution networks.
It provides guidance for determining the:
— effective number of continuous monitoring stations in the drinking water distribution network;
— location of monitoring stations in the drinking water distribution network;
— types of operational and drinking water quality parameter measuring devices (MDs) that can be
installed in a continuous monitoring station;
— quality control, maintenance and calibration requirements of the continuous monitoring system.
This document excludes guidance on the design, structure, number and type of MDs to be installed in a
continuous monitoring system.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 24513, Service activities relating to drinking water supply, wastewater and stormwater systems —
Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 24513 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
accuracy
measurement accuracy
accuracy of measurement
closeness of agreement between a measured quantity value and a true quantity value of a measurand
[SOURCE: ISO/IEC Guide 99:2007, 2.13, modified]
3.2
capability
quality of being able to perform a given activity
[SOURCE: ISO 15531-1:2007, 3.63, modified]
3.3
continuous monitoring
continuous near-real-time measurements of one or more sampling characteristics
Note 1 to entry: To determine the status, it is possible that one or more relevant parameters need to be checked,
supervised, critically observed or measured compared with one or more pre-defined indicators.
Note 2 to entry: Measuring device (3.14) which provides a non-continuous but regular output signal at a given
frequency can be used for the purpose of continuous monitoring.
Note 3 to entry: The location where a measuring device is installed shall be defined as a continuous monitoring
station.
[SOURCE: ISO 2889:2010, 3.22, modified]
3.4
drinking water
DEPRECATED: potable water
water intended for human consumption
Note 1 to entry: Requirements for drinking water quality specifications are generally laid down by the national
relevant authorities. Guidelines are established by the World Health Organization (WHO).
3.5
drinking water distribution network
asset system for distributing drinking water (3.4)
Note 1 to entry: Drinking water distribution networks can include pipes, valves, hydrants, washouts, pumping
stations, reservoirs, and other metering and ancillary infrastructure and components.
Note 2 to entry: Pumping stations and reservoirs can be sited either in the waterworks (3.23) or in the drinking
water distribution network.
3.6
drinking water system
asset system providing the functions of abstracting, treating, storing, distributing or supplying of
drinking water (3.4)
3.7
event
situation when a behaviour deviates from the normal
Note 1 to entry: An event can be one or more occurrences and can have several causes.
Note 2 to entry: An event can consist of something not happening.
Note 3 to entry: An event can sometimes be referred to as an “incident” or “accident”.
Note 4 to entry: An event without consequences can also be referred to as a “near miss”, “incident”, “near hit” or
“close call”.
3.8
event detection
recognition of event indicator or information about a new situation, or both
Note 1 to entry: New situations can be sorted into one of the following:
— event indicator or situation, or both, are considered known and non-hazardous;
2 © ISO 2020 – All rights reserved
— event indicator or situation, or both, are considered hazardous, but a procedure to handle them already exists;
— event indicator or situation, or both, are considered unknown, and a procedure for them does not yet exist.
3.9
event detection process
EDP
set of interrelated or interacting activities which transforms inputs (data or information on an actual or
suspected event (3.7)) into outputs (to support the water utility's (3.22) operational activities)
3.10
event indicator
signal to the water utility (3.22) or one or more stakeholders (3.20) of expectations of service
performance
Note 1 to entry: The signal can exist yet remain unobserved for a period.
3.11
maintenance
combination of all technical, administrative and managerial actions during the life cycle of an asset
intended to retain it in, or restore it to, a state in which it can perform the required function
3.12
management
coordinated activities to direct and control a water utility (3.22)
Note 1 to entry: Management can include establishing policies and objectives, and processes (3.17) to achieve
these objectives.
Note 2 to entry: The word “management” sometimes refers to people, i.e. a person or group of people with
authority and responsibility for the conduct and control of a service. When “management” is used in this sense, it
should always be used with some form of qualifier to avoid confusion with the concept “management” as a set of
activities defined above. For example, “management should …” is deprecated whereas “crisis management team
should …” is acceptable. Otherwise different words should be adopted to convey the concept when related to
people, e.g. managerial or managers.
Note 3 to entry: The term “management” can be qualified by a specific domain it addresses. Examples include
public health management, environmental management and risk (3.18) management.
3.13
measurement
process (3.17) to determine a value
3.14
measuring device
MD
component, or a group of components, used in an in-line or online operating position, which continuously
(or at a given frequency) gives an output signal proportional to the value of one or more measurands in
waters which it measures
Note 1 to entry: The device can be portable or fixed in position.
Note 2 to entry: The term “in-line measuring device” is often used for a measuring device used in an in-line
position. The term “online measuring device” is often used for a measuring device used in an online position.
[SOURCE: EN 17075:2018, 3.1]
3.15
monitoring
determining the status of a system, a process (3.17) or an activity
Note 1 to entry: To determine the status, there can be a need to check, supervise or critically observe.
3.16
operation
action(s) taken in the course of normal functioning of drinking water (3.4) or wastewater systems
EXAMPLE Monitoring and regulation or diversion of drinking water or wastewater.
3.17
process
set of interrelated or interacting activities that use inputs to deliver an intended result
Note 1 to entry: Whether the “intended result” of a process is called an output, product or service depends on the
context of the reference.
Note 2 to entry: Inputs to a process are generally the outputs of other processes and outputs of a process are
generally the inputs to other processes.
Note 3 to entry: Two or more interrelated and interacting processes in series can also be referred to as a process.
Note 4 to entry: Processes in an organization are generally planned and carried out under controlled conditions
to add value.
Note 5 to entry: A process where the conformity of the resulting output cannot be readily or economically
validated is frequently referred to as a “special process”.
Note 6 to entry: In benchmarking, organizational and technical processes and combinations of both are
considered. A process within the meaning of benchmarking comprises a combination of one task with one plant
or object (e.g. operate sewer network, treat wastewater, treat drinking water (3.4), provide domestic connection,
further train staff, purchase material).
Note 7 to entry: In service standards, the term “process” can have a broader meaning than its narrower
interpretation in management system standards. For example, it can also include some elements.
3.18
risk
combination of the likelihood of a hazardous event (3.7) and the severity of consequences, if the hazard
occurs in the drinking water system (3.6), wastewater system or stormwater system
Note 1 to entry: Risk is often characterized by reference to potential events and consequences or a combination
of these.
Note 2 to entry: The English term “likelihood” does not have a direct equivalent in some languages; instead, the
equivalent of the term “probability” is often used. However, in English, “probability” is often narrowly interpreted
as a mathematical term. Therefore, in risk management terminology, “likelihood” is used with the intent that it
should have the same broad interpretation as the term “probability” has in many languages other than English.
Note 3 to entry: Risk can also be defined as the effect of uncertainty on objectives, where uncertainty is the state,
even partial, of deficiency of information related to understanding or knowledge of an event, its consequence or
likelihood.
3.19
sensor
electronic device that senses a physical condition or chemical's presence and delivers an electronic
signal proportional to the observed characteristic
[SOURCE: ISO/IEC TR 29181-9: 2017, 3.14, modified]
4 © ISO 2020 – All rights reserved
3.20
stakeholder
interested party
person or organization that can affect, be affected by or perceive itself to be affected by a decision or
activity
EXAMPLE Users (3.21) and building owners, relevant authorities, responsible bodies, operators, employees
of the operator, external product suppliers and providers of other services, contractors, communities, customers
and environmental associations, financial institutions, scientific and technical organizations, laboratories.
Note 1 to entry: Stakeholders will typically have an interest in the performance or success of an organization.
Note 2 to entry: For the application of this document, environment is considered as a specific stakeholder.
3.21
user
DEPRECATED: consumer
person, group or organization that benefits from drinking water (3.4) delivery and related services,
wastewater service activities, stormwater service activities or from reclaimed water delivery and
related services
Note 1 to entry: Users are a category of stakeholder.
Note 2 to entry: Users can belong to various economic sectors: domestic users, commerce, industry, tertiary
activities or agriculture.
Note 3 to entry: The term “consumer” can also be used, but in most countries the term “user” is more common
when referring to public services.
3.22
water utility
whole set of organization, processes, activities, means and resources necessary for abstracting,
treating, distributing or supplying drinking water (3.4) or for collecting, conveying, treating, disposing
or reusing of wastewater or for the control, collection, storage, transport and use of stormwater and for
providing the associated services
Note 1 to entry: Some key features of a water utility are:
— its mission, to provide drinking water services or wastewater services or the control, collection, storage,
transport and use of stormwater services or a combination thereof;
— its physical area of responsibility and the population within this area;
— its responsible body;
— the general organization with the function of operator being carried out by the responsible body, or by legally
distinct operators;
— the type of physical systems used to provide the services, with various degrees of centralization.
Note 2 to entry: Drinking water utility addresses a utility dealing only with drinking water; wastewater utility
addresses a utility dealing only with wastewater; stormwater utility addresses a utility dealing only with
stormwater.
Note 3 to entry: When it is unnecessary or difficult to make a distinction between responsible body and operator,
the term “water utility” covers both.
Note 4 to entry: In common English, “water service” can be used as a synonym for “water utility”, but this
document does not recommend using the term in this way.
3.23
waterworks
asset system for collecting, treating, pumping and storing drinking water (3.4)
Note 1 to entry: asset types can include catchments, impounding reservoirs, dams, springs, wells, intakes,
transmission mains, filters, tanks, dosing equipment, metering and ancillary infrastructure.
Note 2 to entry: Pumping stations and reservoirs can be sited either in the waterworks or in the drinking water
distribution network (3.5).
4 Principles
Compliance with the requirements for monitoring of drinking water quality and operational
parameters is predominantly achieved using spot sampling and laboratory analysis. The use of MDs
for the continuous monitoring of the drinking water distribution network can be an effective means for
the real-time identification of changes indicating potential contamination of drinking water quality or
events interfering with the operation of a drinking water system. Such real-time identification of events
can improve drinking water supply integrity.
Some MDs can measure several parameters at the same time and can use data analysis tools to facilitate
the reading and understanding of the measurements.
The use of MDs for the continuous monitoring of the drinking water system can provide an effective
supplementary measure within the organization and management of water services.
Although the cost of acquiring MDs will typically be reduced with wider uptake, it should be recognized
that their deployment can be costlier than using sampling and laboratory analysis. Any decision made
to apply MDs should be based on a cost-benefit analysis to ensure that no unjustified cost is transferred
to users. While their deployment should reduce the risk of harm for users, it will not remove the risk
entirely. The installation of MDs should be carefully planned and should only be considered if the water
utility has high confidence that the MDs will reliably detect the chosen parameter(s) to be monitored.
A risk evaluation should be carried out to evaluate the significance of false-positive and false-negative
results from the MD.
The use of MDs can be justified if the system is of added value for risk management and more cost-
effective than the conventional monitoring methods.
Guidance is given on how to deploy a continuous monitoring system. In order to select the location for
MDs properly, the identification of critical control points in the drinking water system is important.
Generally, MD deployment is more likely in larger water mains than further downstream in the narrow
pipes serving individual locations.
Avoidance of harm to service users is the primary reason for the deployment of MDs to detect hazards
arising in the drinking water distribution network. Continuous monitoring can reduce the risk of harm
to users and improve response capability by providing real-time indication of a potentially hazardous
event in a drinking water distribution network.
Research into water security has identified the following critical factors:
— efforts to determine which MDs are useful for detection;
— methods to minimize the time from an event's occurrence to its detection;
— determination of the size of the populations affected;
— minimization of the size of the affected population;
— demand for water that would occur prior to detection and maximization of the likelihood of
detection.
6 © ISO 2020 – All rights reserved
There is the potential of severe public health consequences from the intentional or accidental
introduction of contaminants into the drinking water distribution network. Also, the deterioration of
drinking water quality that can occur due to an event or condition in the drinking water distribution
network, even when no outside contaminants are introduced, can adversely affect public health.
Monitoring plays a crucial role in the provision of reliable drinking water supply to users. While grab
samples and laboratory analysis provide information as to the general status of drinking water quality,
they are not designed to, nor are they capable of, detecting unforeseen or transient events in a timely
manner. As a supplement to laboratory analysis, the continuous monitoring of drinking water quality
and drinking water distribution network operational parameters provide a valuable means to detect
unforeseen and transient events, to help respond to drinking water quality problems and to limit the
consequences of drinking water quality problems.
5 Considerations for the justification of need for continuous monitoring
5.1 General
Continuous monitoring of key drinking water quality and distribution network operational parameters
can serve as an indicator of the presence of contamination in the drinking water via their response or
via their deviation from normal signal levels. The measured parameters can be biological, chemical or
physical in nature.
Furthermore, when the contaminant being detected is unexpected, either via accidental release or
deliberate contamination, continuous monitoring is a practical method to facilitate rapid detection and
to give the chance of a timely response.
Continuous monitoring, field testing and laboratory analysis (offline monitoring) all have advantages
and disadvantages. Depending upon the local context and situation, it is often desirable to employ
continuous monitoring, field testing and laboratory analysis methods in a complementary manner to
make use of the advantages and compensate for the disadvantages of each.
Some examples of the advantages and disadvantages of continuous monitoring against field testing and
laboratory analysis monitoring are described in Table 1.
5.2 Cost-benefit
The number of measurements should be optimized to ensure adequate coverage of the network, thus
minimizing costs while securing an acceptable level of benefits. Dual use benefits are an important
attribute of continuous monitoring. The types and locations for installing MDs should be chosen not only
for achieving the goals of water security but also for helping to achieve objectives such as compliance
and system optimization.
Continuous monitoring systems can be complex. They typically include sampling, analysis,
communication, data storage and data interpretation.
The MDs and data systems require periodic updating and replacement. Continuous monitoring systems
require staff trust in instrument readings and a different skill set than sampling and laboratory
testing to perform operation and maintenance of MDs. Continuous monitoring systems can have high
investment costs and significant operation and maintenance costs.
While continuous monitoring can be expensive, when all its attributes are considered its potential cost-
benefits, particularly in relation to reduced staff and labour costs, should be examined accurately.
Table 1 — Examples of the comparison of monitoring locations and methods in various aspects
Aspect Type of monitoring
Sampling and laboratory Field testing Continuous monitoring
analysis
Parameters that can be High number of param- Not all parameters can be Limited number of param-
monitored eters can be monitored, accurately measured in eters can be measured due
including all regulated the field to technology constraints
parameters
Number of sampling points Limited based on collec- Limited based on labour Limited by cost and main-
tion time and laboratory and throughput tenance
throughput
Frequency of testing Limited based on time and Limited based on labour Can be limited due to lack
laboratory throughput and testing capacity of energy supply and other
possible constraints de-
pending on technology
Time to results Long, can be several hours Moderate, depending on Short, almost instantane-
up to days the test ous real-time
System and equipment High, but most utilities Low equipment needs but High (site, power, commu-
needs already have in place high labour cost nications, data handling)
(e.g. analysers, labware,
facility)
Chemical (reagents) needs Moderate: types of Low volumes and low num- Moderate: usually lower
reagents are high, but vol- ber of types of reagents volume of reagents per test
umes are usually moderate but higher number of tests
Maintenance and calibra- High, but relatively routine High: usually done back at Moderate: relatively rou-
tion and part of standard oper- the utility not in the field tine and part of standard
ation procedures operation procedures
Data reliability High, if it is calibrated and Moderate, if it is calibrated High-low: may vary de-
maintained properly, if and maintained properly, pending on the MD and if it
good laboratory practices if good practices are used is calibrated and main-
are followed; meets regu- may or may not meet regu- tained properly
latory requirements latory needs
Ability to detect drinking Low: good accuracy but Low: just offers a snapshot Moderate: continuous
water quality event limited samples, just offers of conditions real-time but only a limit-
a snapshot ed number of parameters
available
Staff skill level required High: requires skilled Moderate: easier tests Moderate except for cali-
professionals mastered with limited bration and maintenance,
training which can require a higher
skill level
Occupational health and High: hazardous chemicals Moderate: limited number Low except for calibration
safety issues and testing procedures of parameters and de- and maintenance, which
signed to be less hazard- can be contracted out, also
ous for field use requires fewer personnel
5.3 Risks of continuous monitoring
A robust and comprehensive model of the drinking water distribution network as well as a thorough
risk analysis should be used in the selection and optimization of locations for MD placement.
Continuous monitoring systems are an effective means of determining the occurrence and the location
of drinking water quality events in a timely manner, and only a limited number of parameters is
required. However, due to limitations in MD technology, not all contaminants can be detected at levels
that would be detrimental to public health.
See advantages (positives) and disadvantages (negatives) of continuous monitoring systems in Annex A.
8 © ISO 2020 – All rights reserved
5.4 Local contexts
Continuous monitoring systems have advantages and disadvantages compared with laboratory
analysis (offline monitoring). Both should be used complementarily. When installing a continuous
monitoring system, it should be judged whether it can be used sustainably considering local contexts
and situations. The following points should be considered:
— required number of MDs;
— requirements for maintenance and calibration;
— requirements for minimizing exposure to environmental impacts (e.g. weather, radiation from
solar rays);
— responsibilities for maintenance and calibration.
6 Choosing parameters to be monitored
There is no single parameter or combination of parameters that if measured will provide a universal
solution for achieving an acceptable monitoring system for all deployment sites. In most cases the best
choice will be the monitoring of a suite of different parameters that can detect the contaminants that
represent the highest risks in an individual site’s profile.
Characteristics of effective MDs should include:
— cause no adverse effects, either directly or indirectly, on drinking water quality;
— be appropriate for the intended identification of contaminants and operational deviations;
— provide reliable results;
— be aware of local laws and regulatory requirements for contact with drinking water;
— be selected to meet the needs for the detection of drinking water contamination and operational
events.
For a brief description and functions of commonly used and installed drinking water quality parameter
MDs in water utilities see Annex B.
The parameters to be measured should be identified together with their characteristics in relation
to contamination monitoring. The functionality and capabilities of the MDs used to measure these
parameters should be assessed (singly and in combination) for their relevance to the drinking water
distribution network in general and their proposed installation locations in particular.
Some considerations include:
— What is the goal of the drinking water monitoring programme? Drinking water quality parameters
can generally be divided into three types:
— parameters useful for the detection of system upsets and events;
— parameters useful in the day-to-day monitoring and control of drinking water quality;
— parameters that are dual use and serve both of the previous functions.
Based on a drinking water system’s risk profile and monitoring capabilities, dual-use parameters
can be a choice that offers both the capability of detecting unusual drinking water quality events
and controlling and improving daily drinking water quality.
— What is the risk profile of the system being monitored? What is the population density and type of
user in the service area? For example, if the system is located in a heavily industrialized area with
a large petrochemical presence it can be sensible to measure parameters like total organic carbon
(TOC) in drinking water, whereas in a system located on a pristine low-risk water source with little
industry in the area, monitoring these parameters would make less sense.
— What type of MD should be used to measure a given parameter at a specific location? MDs may use
different methods for a particular parameter, for example an electrochemical probe or a colorimetric
method for residual chlorine. Different methods will have different detection levels, and accuracy
statements, calibration intervals and maintenance profiles with associated costs. It is important to
investigate MD options when choosing which parameters to monitor as different methods may or
may not make monitoring for a given parameter practical at a given location.
What type of disinfectant is being utilized? In networks where disinfection residual is being used,
different parameters and MD types will be required, depending on the type of residual disinfectant
utilized. Networks utilizing free chlorine will need to monitor different parameters and use
different MDs than networks that utilize monochloramine as a disinfectant residual. In networks
that do not utilize a residual disinfectant it would make little sense to monitor for these parameters
in the distribution network.
— How can the MD performance be ensured? There are several possibilities to check and ensure that
the performance is adequate and fits the needs of the system in relation to parameters such as
accuracy, repeatability, reliability and other confidence, maintenance and operational parameters,
thus greatly improving user confidence when purchasing MDs:
— testing;
— approval arrangements;
— references from other water utilities that have installed the relevant MDs (see Annex C).
NOTE Not all drinking water quality parameter MDs for specific purposes are reviewed in this document.
For more information, see “Monitoring water quality in the drinking water network” published by the federation
[10]
of Canadian Municipalities , which includes a more complete review of water quality continuous MDs.
MDs can be responsive to changes in operational parameters of the drinking water distribution
network. Therefore, if continuous measurement devices for operational parameters are installed in a
drinking water distribution network, their readings should be taken into consideration when analysing
the drinking water quality parameters' readings.
See how operational parameters can influence drinking water quality measurements on Table 2.
10 © ISO 2020 – All rights reserved
Table 2 — Operational parameter measurements that can influence drinking water quality
measurements
Operational parameter measured by the MD Influence on drinking water quality measurements
Flow Flow meter data can be used for the identification and
analysis of drinking-water-quality-related factors,
e.g
...
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