ISO/TS 24522:2019

Event detection process: Guidelines for water and wastewater utilities

This document provides guidance for water utilities on the detection and classification of water and wastewater events. The following subjects are within the scope of this document: — publicly and privately owned and operated water utilities. It does not favour any particular ownership or operating model; — all aspects of the drinking water system and the wastewater system; — all causes of abnormal changes in water and/or wastewater service provision capable of detection by monitoring systems including accidents, unexpected operational changes, natural hazards and intentional disruption. This document is independent of the measurement methods used to collect the data. The document focuses on events which could imminently affect the water utility's interested parties. The following are outside the scope of this document: — methods of design and construction of drinking water and wastewater systems; — plumbing and drainage systems not under the control of the water utility. This document does not include details about action taken as a result of event detection. For such details see ISO 24518 and EN 15975 Part 1.

Titre manque

General Information

• Status: Published
• Publication Date: 26-Feb-2019
• ICS: 03.080.30 - Services for consumers
• ICS: 13.060.20 - Drinking water
• ICS: 13.060.30 - Sewage water
• Technical Committee: ISO/TC 224 - Drinking water, wastewater and stormwater systems and services
• Drafting Committee: ISO/TC 224 - Drinking water, wastewater and stormwater systems and services
• Current Stage: 9093 - International Standard confirmed
• Start Date: 03-Sep-2025
• Completion Date: 13-Dec-2025

Overview

ISO/TS 24522:2019 - "Event detection process: Guidelines for water and wastewater utilities" provides practical guidance for designing, implementing and reviewing an Event Detection Process (EDP) used by drinking water and wastewater utilities. It describes how to detect and classify abnormal changes in service provision (accidents, operational changes, natural hazards, intentional disruption) using monitoring and sampling data. The guidance is measurement‑method independent and is aligned with WHO Water Safety Plan and Sanitation Safety Planning approaches.

Key topics and technical requirements

• EDP lifecycle: Design phase, Detection phase and Ongoing activities (post‑event evaluation, periodic review, validation).
• Inputs and tools:
  • Influence Matrix Table (IMT) and Event Identification Table (EIT) for mapping indicators to potential events.
  • Lists of typical event indicators (sensor signals, lab results, operational alarms).
  • Grouping of signal measurements and handling of missing or unfamiliar inputs.
• Event classification and evaluation:
  • Process‑based classification, assignment of weights, frequency and confidence calculations, and classification performance estimation.
  • Guidance on validation, confidence‑level assignment and statistical methods for assessing classification efficiency.
• Operational controls:
  • Notification workflows, timestamping and secure documentation of events.
  • Governance: access control, user training, testing and output presentation.
• Automation considerations: Guidance on when automated decision‑making may be appropriate and when manual oversight is required.
• Annexes and tools: Examples (IMT, EIT), statistical evaluation methods, grouping strategies and verification procedures to test EDP responsiveness.

Applications and who should use it

ISO/TS 24522 is intended for:

• Water and wastewater utility managers (operations, asset, quality and incident teams) implementing event detection systems.
• Engineers and system integrators designing monitoring/sensor networks and analytics for utilities.
• Consultants and auditors assessing utility preparedness and detection capability.
• Regulators and emergency planners who need a consistent framework for evaluating utility detection and notification practices. Practical uses include designing detection rules, improving alarm thresholds, validating classification performance, and documenting detection procedures to support timely alerts and risk‑based decision making.

Related standards

• ISO 24518 - Guidance on actions after event detection (referenced for response actions).
• EN 15975‑1 - Security of drinking water supply - aspects of response (see for response details).
• WHO Water Safety Plan and Sanitation Safety Planning - risk‑based approaches that this TS complements.

Keywords: ISO/TS 24522, event detection process, EDP, water utilities, wastewater utilities, event classification, monitoring systems, influence matrix, event indicators, WHO Water Safety Plan.

Standards Content (Sample)

TECHNICAL ISO/TS
SPECIFICATION 24522
First edition
2019-02
Event detection process: Guidelines
for water and wastewater utilities
Reference number
©
ISO 2019
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principles of an event detection process . 5
4.1 Design phase . 5
4.1.1 General. 5
4.1.2 Influence matrix table and EDP . 6
4.1.3 EDP inputs . 7
4.1.4 EDP design . 7
4.1.5 EDP target service level design . 8
4.2 Detection phase . 8
4.2.1 General. 8
4.2.2 Validation process . . . 8
4.2.3 Further event monitoring . 9
4.3 Ongoing activities . 9
4.3.1 Post-event EDP evaluation . 9
4.3.2 Periodic reviews . 9
4.3.3 Validation of links between phenomena and risk materialization .10
4.3.4 Estimation.10
4.3.5 Decision-making .10
4.3.6 Guidance on interpretation .10
5 The event detection cycle and the role of the EDP .10
5.1 The EDP's application of the event detection cycle (the EDP cycle) .10
5.2 Development and regular review of an EDP-based event detection capability .11
5.2.1 General.11
5.2.2 Listing of possible event indicators .12
5.2.3 IMT establishment . .12
5.2.4 EIT establishment .12
5.2.5 IMT and EIT periodic review .12
5.3 Deployment of an event detection procedure .12
5.3.1 General.12
5.3.2 Defining the possibility of an event's occurrence .13
5.3.3 Nature of water/wastewater measurement sampling considerations .13
5.3.4 Results assessment .13
5.3.5 Missing inputs .14
5.3.6 Unfamiliar combination of inputs .14
5.3.7 Deviation from normal frequency detection .14
5.3.8 Measurement grouping .14
5.4 Classification of events and evaluation of the classification procedure .14
5.4.1 General.14
5.4.2 Process-based classification .15
5.4.3 Actual classification .15
5.4.4 Assignment of weights .16
5.4.5 Frequency calculations .16
5.4.6 Classification efficiency estimation .16
5.4.7 Classification evaluation .16
5.5 Notification to relevant personnel/systems .16
5.6 Documentation of events .16
5.6.1 General.16
5.6.2 Time stamps.17
5.6.3 Subsequent documentation .17
5.6.4 Responsible person documentation .17
5.6.5 Documentation authority .17
5.6.6 Data security . .17
5.7 Validation process — Periodic evaluation of the detection process .17
5.7.1 General.17
5.7.2 Confidence-level assignment .17
5.8 Periodic system evaluation — System functionality .18
5.9 EDP development — General principles and governance .18
5.9.1 EDP operation .18
5.9.2 Access to the EDP .18
5.9.3 User training and qualification .18
5.9.4 Testing and certification .19
5.9.5 EDP output expression .19
5.9.6 EDP output presentation .19
Annex A (informative) Examples of typical event indicators that could be used as EDP inputs .20
Annex B (informative) Influence matrix table (IMT) .27
Annex C (informative) Event identification table (EIT) .31
Annex D (informative) Examples of statistical methods for the evaluation of event
classification within the EDP .37
Annex E (informative) Signal measurements' grouping .43
Annex F (informative) Verifying the EDP’s response to potential types of events .45
Annex G (informative) Classification of potential events detected .48
Annex H (informative) Event classification performance guide .53
Bibliography .55
iv © ISO 2019 – All rights reserved

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.
Introduction
This document has been created in response to an international demand for guidelines on the
development of an event detection process (EDP) for drinking water and wastewater utilities (water
utilities). The EDP is a key element of a water utility's wider event detection system. That system relies
on, and is interrelated to, the water utility's sensor and sampling systems.
This document aims to support water utilities in the development of an EDP that monitors the relevant
variables across their water/wastewater services and evaluates changes in those variables that can
suggest an event has either occurred or could be imminent.
This document aims to be consistent with both the World Health Organization (WHO) Water Safety
Plan approach for water supply and the WHO Sanitation Safety Planning approach for wastewater
collection, treatment and disposal or reuse. Both take a risk-based approach to evaluating uncertainty
about the quality and significance of data that suggests the occurrence of an event.
NOTE 1 This document addresses a wider range of event causation than that implied by the definition of
‘hazard’ in the WHO manuals.
For example (water): a change in the hardness of the water supplied could remain within acceptable limits for
public health purposes but could still represent a change in water quality of material interest to some service
users (e.g. breweries).
For example (wastewater): ingress of a volatile chemical into the wastewater system ought not to represent
a direct health hazard in all circumstances, but, depending on its concentrations, could result in an explosion
within the network or fire damage to the wastewater infrastructure.
Outputs from an EDP could help inform those within the water utility responsible for identifying events
and alerting individuals responsible for event response decision-making. Such alerts could be required
despite uncertainty about the quality and reliability of the data currently available.
Event response decisions can be based on those decision makers’ knowledge, experience and
assessment of the cause(s) and effect(s) of the event as it unfolds – including consideration of the EDP’s
outputs where appropriate.
At the discretion of the water utility, design of the EDP could incorporate elements of automated
decision-making.
NOTE 2 If automated decision-making is proposed, consideration could require distinguishing between
situations where automation could be appropriate and those where it would not be. For example, automation
with low-impact outcomes could be acceptable but automation with high-impact outcomes could require greater
caution. When considering automation, it is advisable to consider the appropriateness of inputs, the complexity
of the system, the nature of the water utility and the effect of time delays.
A decision on whether to implement the water utility’s procedure for dealing with an abnormal situation
could be required in response to an identified or suspected event.
Such a decision could depend upon the confidence in the EDP’s classification and output and the process
underpinning it.
The guidelines could be of particular use to those water utilities that wish to enhance their ability to
recognize abnormal events as a means to: maintain or improve public health provision; improve their
operational processes; enhance the levels of their service provision; or reduce risks to the continued
delivery of existing service levels.
In addition, development of an EDP can be a valuable aid to organizational learning and memory. The
existence of an effective and efficient EDP provides a significant control against the risk of loss of
individuals’ knowledge and expertise by increasing a water utility’s independence from such vulnerable
resources. Regular use and review of an EDP’s successes and failures can contribute to organizational
learning and a reduction in the time taken to detect an event.
vi © ISO 2019 – All rights reserved

TECHNICAL SPECIFICATION ISO/TS 24522:2019(E)
Event detection process: Guidelines for water and
wastewater utilities
1 Scope
This document provides guidance for water utilities on the detection and classification of water and
wastewater events.
The following subjects are within the scope of this document:
— publicly and privately owned and operated water utilities. It does not favour any particular
ownership or operating model;
— all aspects of the drinking water system and the wastewater system;
— all causes of abnormal changes in water and/or wastewater service provision capable of detection
by monitoring systems including accidents, unexpected operational changes, natural hazards and
intentional disruption.
This document is independent of the measurement methods used to collect the data.
The document focuses on events which could imminently affect the water utility’s interested parties.
The following are outside the scope of this document:
— methods of design and construction of drinking water and wastewater systems;
— plumbing and drainage systems not under the control of the water utility.
This document does not include details about action taken as a result of event detection. For such details
see ISO 24518 and EN 15975 Part 1.
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, Activities relating to drinking water, wastewater and stormwater services — 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
classification
category that the event (3.5) falls into
3.2
continual improvement
recurring activity to enhance performance (3.15)
Note 1 to entry: The process (3.16) of establishing objectives (3.13) and finding opportunities for improvement
is a continual process through the use of audit findings and audit conclusions, analysis of data, management
reviews or other means and generally leads to corrective action or preventive action.
Note 2 to entry: The nature of the activity can differ between cycles of recurrence.
[SOURCE: ISO 9000: 2015, 3.3.2, modified — Note 2 to entry replaced.]
3.3
documented information
information required to be controlled and maintained by an organization (3.14) and the medium on
which it is contained
Note 1 to entry: Documented information can be in any format and media and from any source.
Note 2 to entry: Documented information can refer to:
— the management system, including related processes (3.16);
— information created in order for the organization (3.14) to operate (documentation);
— evidence of results achieved (records).
3.4
effectiveness
extent to which planned activities are realized and planned results are achieved
3.5
event
situation where 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”.
Note 5 to entry: For the purposes of this document, “normal” refers to what is expected.
3.6
event detection
recognition of event indicator (3.9) and/or information about a new situation
Note 1 to entry: New situations can be sorted into one of the following:
— event indicator and/or situation(s) are considered known and non-hazardous;
— event indicator and/or situation(s) are considered hazardous, but a procedure to handle them already exists;
— event indicator and situation(s) are considered unknown, and for which a procedure does not yet exist.
3.7
event detection process
EDP
set of interrelated or interacting activities which transforms inputs [data or information on an actual or
suspected event (3.5)] into outputs [to support the water utility’s (3.19) operational activities]
2 © ISO 2019 – All rights reserved

3.8
event identification table
EIT
table developed by the organization (3.14) that contains examples of proven connections between
changes in water measurements and possible causation types
3.9
event indicator
signal to the water utility or one or more stakeholders (3.18) that an event (3.5) can have occurred with
the potential to cause a significant deviation in the users' expectations of service performance (3.15)
Note 1 to entry: The signal can exist yet remain unobserved for a period.
3.10
influence matrix table
IMT
table developed by the water utility (3.19) that contains suspected connections between event
indicators (3.9) and performance measurements (3.11) based on scientific knowledge and water industry
experience
3.11
measurement
process (3.16) to determine a value
3.12
monitoring
determining the status of a system, a process (3.16) or an activity
Note 1 to entry: To determine the status there can be a need to check, supervise or critically observe.
3.13
objective
result to be achieved
Note 1 to entry: An objective can be strategic, tactical or operational.
Note 2 to entry: Objectives can relate to different disciplines (such as finance, health and safety, and environmental
goals) and can apply at different levels [such as strategic, organization-wide, project, product and process (3.16)].
Note 3 to entry: An objective can be expressed in other ways, for example as an intended outcome, a purpose, an
operational criterion, an event detection objective or by the use of other words with similar meaning (e.g. aim,
goal or target).
Note 4 to entry: In the context of an event detection system, event detection objectives are set by the water utility
(3.19), consistent with the event detection management policy, to achieve specific results.
3.14
organization
person or group of people that has its own functions with responsibilities, authorities and relationships
to achieve its objectives (3.13)
Note 1 to entry: The concept of organization includes, but is not limited to, sole-trader, company, corporation,
firm, enterprise, authority, partnership, association, charity or institution, or part or combination thereof,
whether incorporated or not, public or private.
Note 2 to entry: For the purposes of this document the organization responsible for event detection (3.6) will
usually be part of a wider organization [the water utility (3.19) responsible for the provision of drinking water/
wastewater services].
3.15
performance
measurable result
Note 1 to entry: Performance can relate either to quantitative or qualitative findings.
Note 2 to entry: Performance can relate to the management of activities, processes (3.16), products (including
services), systems or organizations (3.14).
3.16
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 (3.14) 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”.
3.17
risk
combination of the likelihood of a hazardous event and the severity of consequences, if the hazard
occurs in the drinking water system or wastewater system
Note 1 to entry: Risk is often characterized by reference to potential events (3.5) 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
has 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 (3.13), where uncertainty is
the state, even partial, of deficiency of information related to understanding or knowledge of an event (3.5), its
consequence or likelihood.
3.18
stakeholder
interested party
person or organization (3.14) that can affect, be affected by or perceive itself to be affected by a decision
or activity
EXAMPLE Users 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 (3.14), laboratories.
Note 1 to entry: Stakeholders will typically have an interest in the performance (3.15) or success of an
organization.
Note 2 to entry: For the application of this document, environment is considered as a specific stakeholder.
4 © ISO 2019 – All rights reserved

3.19
water utility
whole set of organization (3.14), processes (3.16), activities, means and resources necessary for
abstracting, treating, distributing or supplying drinking water, for collecting, conveying, treating,
disposing of and reusing wastewater or for the control, collection, storage, transport and use or disposal
of stormwater and for providing the associated services
Note 1 to entry: Some key features for 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 (3.14) with the function of operator being carried out by the responsible body, or by
legally distinct operator(s);
— 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 not necessary or it is 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.
4 Principles of an event detection process
4.1 Design phase
4.1.1 General
The water utility should determine the scope of the event detection process (EDP)'s detection
capabilities. This should include:
— all credible events identified via the risk assessment process;
— the ability to respond promptly to unanticipated events (actual or suspected).
The scope should be available as documented information.
The range of complexity of the EDP chosen can vary from manual data analysis of paper-based historical
records through to a fully computerized system. The level of complexity chosen should be consistent
with the water utility’s local conditions, to avoid unrealistic assumptions about the adequacy of the
EDP’s outputs.
The EDP's design should be based on a methodology to detect the possibility of the occurrence of events;
perform analysis of incoming data to identify and classify possible events; and contain a validation
process to constantly ensure quality of detection and classification.
Events can be water- or wastewater-related, and have water or wastewater quality consequences or
other consequences (e.g. physical ones such as pressure or flow fluctuations, or operational ones such
as chlorinous taste or foul odour complaints).
An EDP should aim to detect the occurrence of an event, provide guidance as to the event‘s likely cause
and assist in the classification of the event's severity, urgency and possible consequences (see Figure 1).
The extent to which an EDP should be capable of distinguishing between the severity and urgency
components of abnormal conditions should be a key consideration in the design phase.
Such guidance should permit the description of one or more possible risks (by postulating one or more
chains of cause/effect/consequence).
The effectiveness of the EDP’s design and the efficiency of its application should thus reduce the
uncertainty surrounding possible alternative causes of an event pending actual confirmation of the cause.
To be successful, event detection should rely on the water utility‘s prior establishment of effective
control over and conformity with warning values and limit values and their incorporation into
operating procedures.
Since the EDP is based mainly on statistical analysis, the water utility should be aware that the existence
of an EDP cannot guarantee that the event‘s causation and consequences for service provision will
always be recognized before any interested party is affected or that the cause will always be quickly
identified.
Key
Figure 1 — Illustration of the relationship of the influence matrix table (IMT) to the event
identification table (EIT) in the event detection process (EDP)
4.1.2 Influence matrix table and EDP
Event indicators are a list of measurable indicators based on available knowledge that would change
when an identified risk actually occurs (Annex A contains examples of some typical event indicators
that could be used as EDP system inputs).
System inputs should be used to construct a tool (e.g. table or flow chart) – described henceforth as
an influence matrix table (IMT) – related to the water utility's function(s). The IMT should describe
6 © ISO 2019 – All rights reserved

the relationship(s) between individual inputs (event indicators) and their hypothesized, suspected
or “known” (in a probabilistic sense) effect(s). Annex B contains examples of water and wastewater
IMT. The relationship between the IMT and the event identification table (EIT) is described here. Their
relative positioning within the EDP is described in 5.2.3 and 5.2.4, and illustrated in Figure 3.
The content of the IMT should provide inputs to the process of constructing an EIT in three stages.
Firstly, the IMT should contain an “if”/”then” relationship(s) between changes in event indicator
measurements and the effects becoming evident in the system they are indicative of.
Secondly, the water utility can then, by identifying a further set of “if”/”then” effect combinations,
postulate possible causes for these simultaneous effects — progressively refining its analysis by
causation type(s) (identifying unique or possible alternative causation options).
Thirdly, the IMT should contain a value and timestamp a value.
Table C.1 in Annex C contains examples of simultaneous relationships which could form part of an EIT's
content.
It can be seen in Figure 1 that the IMT is the starting point, first to look “downstream” in the indicator/
effect relationship(s) and then, by combining knowledge of simultaneous effects causation, to look
“upstream” to (with increasing maturity as the EDP develops) hypothesize, propose or predict a
suspected event’s cause.
NOTE The probability of successfully identifying causation is likely to increase with the developing maturity
of the EDP. This maturity is likely to arise from refinement of the "if"/"then" rules created in the IMT and the EIT.
The former’s rules are likely to have a high degree of commonality across water utilities and be relatively easy to
establish from literature. The latter will vary between water utilities depending on a range of factors and require
more local knowledge. Ultimately a fully mature EDP will be unique to an individual water utility. By that stage
the IMT and the EIT ought to be capable of referencing specific locations and indicator measurements associated
with a prediction of causation of individual events affecting the water utility.
4.1.3 EDP inputs
The EDP requires one or more inputs before it can generate an output. The input(s) derived from
operating a water supply/wastewater system could depend on the:
— size of the system,
— system management resources available;
— system management resources’ capabilities;
— economic state of the system;
— size and structure of the water utility's service area;
— infrastructure of the water utility's service area;
— technical state of the system and the level of automation.
4.1.4 EDP design
The design considerations of the EDP should include:
— preferred time frame in which each event should be detected and classified;
— severity and order of priority in which events should be handled;
— number of inaccurate event detection alerts to be tolerated (by location and type) over a defined
period of time [known as false positive (FP) or false negative (FN) alarms — see Annex D].
NOTE Acceptable levels of FP and FN alarms could change over time due to changes in the hazard(s) to which
the water utility is exposed.
Some of the event indicators listed in Annex A are among those that could be identified and used to
establish a target service level for detection by the EDP.
The EDP target service level for detection should be a sub-set of the utility’s general objectives
regarding the provision of water/wastewater services. For further details see ISO 24510, ISO 24511 and
ISO 24512.
4.1.5 EDP target service level design
Given the potential for an event to escalate into a crisis, the EDP target service level for event detection
should be designed to support achievement of the minimum levels of service determined by the utility.
Considerations should include:
— the EDP’s required availability and the acceptability of any planned unavailability;
— the availability of staff competent to operate the EDP and interpret its outputs within and outside
normal working hours;
— the EDP’s resilience to loss or disruption of its normal operating facilities;
— the water utility's capability to restore an acceptable level of the EDP’s functionality within the
maximum tolerable period of disruption determined by the water utility‘s business continuity
management policy.
For further details see ISO 24518, ISO/TS 24520 and EN 15975-1.
4.2 Detection phase
4.2.1 General
There may be several ways to detect an event’s occurrence based on the event indicators. Clause 5
contains a methodology for constructing an EDP that seeks to capture all these opportunities.
Awareness of and access to regular performance measurements undertaken by the water utility should
support the detection of water/wastewater quality changes.
4.2.2 Validation process
Data’s suitability as a dataset input could require a two-step validation process before any further
analysis.
Failure to satisfy all of Step 1’s validation should preclude progress to Step 2.
Step 1: The readings should represent actual reflections of field values. The six basic data validations are:
— physical limits are not violated;
— data are not ‘frozen’;
— essential data are not absent;
— rates of change in that variable remain credible;
— duration of the change in the variable is significant;
— no fixed repetitive patterns are present.
8 © ISO 2019 – All rights reserved

Step 2: Each variable presented should then be analysed separately to see how it is now behaving
compared with historical data trends. In this process, relevant seasonal factors, hours of the day or
day of the week (e.g. reflective of industrial routines) should be considered together with human
behaviour. Technical problems or changes in the operational processes should also be considered where
appropriate.
If any variable is deviating from its historical trend, normal boundaries, rate of change or develops
fixed repetitive patterns (given local consideration of time and season), then reference should also be
made to the EIT to see if it contains rules justifying an alert based on this variable.
Visible inspection of the single data charts may support abnormal condition identification. Design of
the EDP should not preclude continued access to visible inspection of data charts (see EDP verification
methods in Annex F).
In the case of wastewater, information regarding abnormal discharge of industrial material to the
public network should also be taken into consideration.
4.2.3 Further event monitoring
Decisions on further event monitoring to be undertaken should be made, based on the initial alert,
ongoing uncertainties and accumulating knowledge of the unfolding event.
If no escalation is required it may still be desirable to undertake further monitoring as part of the water
utility’s quality assurance process using the ‘Plan, Do, Check, Act’ cycle. For further details see ISO
24510, ISO 24511 and ISO 24512.
If escalation is required, the type and extent of further monitoring should be established as part of
the operational management system. Where the event may require a crisis management response,
the escalation should form part of the ‘pre-crisis phase’ of the crisis management system. For further
details of how the EDP should align with the crisis management system see ISO 24518.
4.3 Ongoing activities
4.3.1 Post-event EDP evaluation
Post-event evaluation of the EDP should establish whether the prediction was accurate, inaccurate or
ambiguous. This evaluation should consider both inputs and outputs, and possible uniqueness of the
water utility, in an attempt to establish the validity of the output. This should result in an updating of
the documented information and continual improvement of the EDP.
NOTE Annex C illustrates varying levels of complexity in the EDP for both water and wastewater utilities.
4.3.2 Periodic reviews
The vulnerability of the drinking water/wastewater system should be periodically reviewed. This
review should include consideration of the list of potential risks derived from the methodology
identified in 4.1.2.
[22]
NOTE For more details of this approach see the WHO Guidelines for drinking-water quality (or the WHO
[23]
Guidelines on sanitation and health ) and EN 15975-2.
The detection process should be evaluated periodically in order to address two aspects:
— does it look at the most relevant event indicators with respect to the possible risks it tries to assess?;
— what is the reliability of its answers?
Assuming satisfactory answers to these two questions, the process can be utilized with confidence to
classify events as positive (i.e. a real eve
...