Participant workbook | Water Safety Plans

Participant workbook

Water Safety Plans – Training package

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International Water Association (IWA)

The International Water Association is a global reference point for water professionals, spanning the

continuum between research and practice and covering all facets of the water cycle. Through its network of

members and experts in research, practice, regulation, industry, consulting and manufacturing, IWA is in a

better position than any other organisation to help water professionals create innovative, pragmatic and

sustainable solutions to challenging global needs. The strength of IWA lies in the professional and geographic

diversity of its membership – a global mosaic of national, corporate and individual member communities. This

publication does not represent the views of the IWA membership as a whole and does not constitute the

formal policy of IWA. IWA takes no responsibility for the result of any action taken on the basis of the

information herein. IWA is a company registered in England No. 3597005. Registered Charity (England) No.

076690.

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iii

WSP Participant Workbook

Contents

Glossary of terms and abbreviations ................................................................................................................. iv

Introduction ........................................................................................................................................................ 1

How to use this workbook .................................................................................................................................. 1

Competence wheel exercise (Part I) ................................................................................................................... 2

Learning material ................................................................................................................................................ 3

WSP introduction (Module 0) ......................................................................................................................... 3

Module 1 – Assemble the WSP team ............................................................................................................. 8

Module 2 – Describe the water supply system............................................................................................. 11

Module 3 – Identify hazards and hazardous events and assess the risks ..................................................... 14

Module 4 – Determine and validate control measures, reassess and prioritize the risks ............................ 18

Module 5 – Develop, implement and maintain an improvement/upgrade plan ......................................... 22

Module 6 – Define monitoring of the control measures .............................................................................. 26

Module 7 – Verify the effectiveness of the WSP .......................................................................................... 30

Module 8 – Prepare management procedures ............................................................................................ 33

Module 9 – Develop supporting programmes .............................................................................................. 36

Module 10 – Plan and carry out periodic review of the WSP ....................................................................... 39

Module 11 – Revise the WSP following an incident ..................................................................................... 42

WSP quality assurance tool (Module 12) ...................................................................................................... 46

Competence wheel exercise (Part II) ................................................................................................................ 49

Essential resources ........................................................................................................................................... 50

Acknowledgements .......................................................................................................................................... 51

Appendix A: Walkerton water tragedy – Module 6 exercise ............................................................................ 52

Appendix B: Quotations for Module 9 exercise ................................................................................................ 55

iv

Glossary of terms and abbreviations

Audit – review and evaluation of WSP practice

Catchment – drainage basin / watershed – a discrete area of land that has a common drainage system. A

catchment includes both water bodies that convey the water and the land surface from which water drains

into these bodies (Helmer & Hespanhol, 1997).

Compliance – adherence to set water quality / operational requirements

Control measure – any action or activity that can be used to prevent, eliminate or reduce to an acceptable

level any water safety hazard

Control point – A step at which control can be applied to prevent, eliminate or reduce the risks of a water

safety hazard

Corrective action – any action to be taken when critical limits are exceeded

Critical limit – a criterion that separates acceptability from unacceptability

HACCP (hazard analysis and critical control points) – a system that identifies, evaluates and controls hazards

that are significant for food safety

Hazard – any agent (physical, chemical, biological or radiological) that can cause harm to public health

Hazardous event – any process that introduces hazards to, or fails to remove them from, the water supply

Implementation (of WSP) – putting a WSP into practice

Incident/near-miss – where loss of control has led to (or narrowly missed) a public health risk

IWA – International Water Association

Monitor – the act of conducting a planned sequence of observations or measurements of control parameters

to assess whether the control point is under control or whether the water meets quality criteria

Multi-barrier approach – the concept of using more than one type of barrier or control measure in a water

supply system (from catchment through abstraction, treatment, storage and distribution to the consumer) to

minimize risks to the safety of the water supply

Operational monitoring – The act of conducting a planned sequence of observations or measurements of

control parameters to assess whether a control measure is operating within design specifications

Operational step – a point, procedure, operation or stage in the water supply process

Organizational culture – attitudes, experiences, norms, beliefs and values of an organization

Point of use – point of consumption

Regulator – organization responsible for ensuring that water supply meets specified statutory requirements

Risk – the likelihood of identified hazards causing harm to exposed populations in a specific time frame and

the magnitude and/or consequences of that harm

Stakeholders – individuals or organizations that are influenced by, or influential to, the water supply

Supporting programmes – actions that are important in ensuring drinking-water safety but do not directly

affect drinking-water quality (e.g. training and management practices)

Upgrade – improvement (to supply system)

v

Validation – investigative activity to identify the effectiveness of control measures. It provides the evidence

that elements of the WSP can effectively meet the water quality targets

Verification – the application of methods, procedures, tests and other evaluations to determine compliance

with the WSP. Verification confirms that the water quality targets are being met and maintained and that the

system as a whole is operating safely and the WSP is functioning effectively.

Water safety plan (WSP) – a comprehensive risk assessment and risk management approach that

encompasses all steps in water supply, from catchment to consumer

WHO – World Health Organization

1

Introduction

This workbook is designed to be used by participants attending a water safety plan (WSP) training workshop

that has been organized around the materials developed by the International Water Association (IWA) and

World Health Organization (WHO). The learning material included in this workbook relates explicitly to the

theory sessions that will be presented and the designed exercises. It therefore cannot be used as a standalone

document to train people on all WSP aspects.

WSPs are a risk-based approach to most effectively protect drinking-water safety. WHO’s 4th edition of the

Guidelines for drinking-water quality (WHO, 2011) explicitly states the importance of WSPs, and the Bonn

Charter (IWA, 2004) advocates the use of WSPs as the best way of ensuring good, safe drinking-water.

WSPs are now being adopted worldwide, but they are not always fully understood by all stakeholders. There

are a number of key terms and concepts that are not always translated appropriately or are simply

misunderstood. Face-to-face training is therefore considered to be an essential component of globally

successful WSP implementation.

The workshop is structured around 13 learning modules. The first module (Introduction) gives an overview of

WSPs. The last module (Module 12) introduces participants to the quality assurance tool for WSPs (WHO &

IWA, 2012). Modules 1–11 relate explicitly to the WSP manual produced by IWA and WHO (Bartram et al.,

2009), from which the workshop is designed.

How to use this workbook

The workbook is structured into 13 modules. Within each module, the learning objectives, key points and

exercise details are included. The workbook is designed to be used during the theory sessions and group work.

Therefore, “answers” are not given to topics discussed during the workshop, but instead space is made

available for the participant to summarize key points from any given activity.

Icons are used throughout the workbook as a guide to the participant on the type of activity. For example, the

following informs the participant that there will be a discussion on how catchment control measures are

assessed:

How can catchment control measures be assessed?

________________________________________________________________________________________

Icon Meaning

Question mark: question is asked. Write answers in workbook

People: group work/activity

People with speech bubble: discussion time

Two people: work in pairs

Flipchart: some information is recorded on a flipchart – transfer to workbook if desired

One person: individual work

2

Competence wheel exercise (Part I)

Score your agreement with the following six statements (A–F). This is for your own use only. The exercise will

be completed again later on in the workshop.

A. I have a thorough understanding of what is involved in WSP design and implementation.

B. I know what hazards and hazardous events are likely to occur in the water supply system where I

work.

C. I have a thorough understanding of the complexities of risk assessment and know of the two main

approaches.

D. I know how a WSP is used to steer financial investments within the utility where I work.

E. I know what a control measure is and how it is used, monitored and validated.

F. I know when a WSP should be reviewed and amended.

For each question, assign a score between 0 and 3:

0 = No understanding and/or not heard of

1 = Little understanding and/or could not apply in practice

2 = Good understanding and/or could apply in practice

3 = Complete understanding and/or have applied in practice and/or could train others

Enter your scores on the wheel diagram below.

0

1

2

3

A

B

C

D

E

F

3

Learning material

WSP introduction (Module 0)

Learning objectives

Through active participation in and successful completion of the introductory module, each participant should

be able to meet the following learning objectives:

• Explain that a WSP is a source to point-of-use risk management approach that exists within a wider

framework for safe drinking-water.

• Explain why the traditional end-product monitoring approaches are insufficient for ensuring drinking-

water safety.

• Elaborate on why the WSP approach was developed and why it is needed.

• Clearly communicate the WSP approach as outlined in the WHO/IWA WSP manual.

Figure 0.1 – WSP steps

Key references:

• Bartram et al. (2009) Water safety plan manual

http://www.wsportal.org/wspmanual

http://www.who.int/water_sanitation_health/publication_9789241562638/en/index.html

• IWA (2004) Bonn charter for safe drinking water

http://www.iwahq.org/cm

Assemble team

(Module 1)

Develop supporting

programmes

(Module 9)

Plan & carry out

periodic WSP review

(Module 10)

Verify the

effectiveness of the

WSP

(Module 7)

Develop, implement

& maintain an

improvement plan

(Module 5)

Determine & validate

control measures,

reassess & prioritize

risks (Module 4)

Identify the hazards &

hazardous events &

assess the risks

(Mod

ule 3)

Revise WSP

following incident

(Module 11)

Describe the water

supply system

(Module 2)

Define monitoring of

control measures

(Module 6)

Feedback

Management & communication

Monitoring

System

a

ssessment

Prepare

management

procedures

(Module 8)

incident

Preparation

4

• WHO (2011) Guidelines for drinking-water quality, 4th edition

http://www.who.int/water_sanitation_health/dwq/guidelines/en/index.html

• WHO (2012) Water safety plan quality assurance tool v1.3 (Excel tool and manual)

http://www.wsportal.org/templates/ld_templates/layout_1367.aspx?ObjectId=20686&lang=eng

http://www.who.int/water_sanitation_health/publications/wsp_qa_tool/en/index1.html

• WSPortal (tools and case-studies)

http://www.wsportal.org

Key points

Principles and features

• WSPs are based on risk management principles from other approaches, including HACCP (hazard

analysis and critical control points) and the multi-barrier approach.

• The WSP approach is applicable to all types of water supply systems.

• End-point monitoring is still important in verifying drinking-water safety. However, a complementary

approach is also needed to lower the risk of contaminants from entering drinking-water supplies in the

first place to better protect consumers.

• WSPs involve preventive risk analysis and risk management from catchment to point of use.

• The public’s health can be protected by knowing the supply system thoroughly, understanding utility

staff roles, being aware of what problems may occur and taking action to control those problems to

result in more consistent supplies of safe drinking-water.

• WSPs require an understanding that is beyond the “technical” aspects (e.g. managerial, training and

incident response).

• WSP objectives are to:

o Minimize contamination in source waters

o Reduce or remove contamination by treatment

o Prevent contamination during storage, distribution and handling.

• The development and implementation of WSPs are a continuous incremental process, with

improvements made over time according to the significance of the risks, available resources, knowledge

and as required. Some utilities may be more experienced in identifying and managing risks (i.e. risk

“mature”) than others, but each can improve, and should improve, continuously over time at a suitable

pace.

• Multiple barriers (more than one control measure) should be put in place from the catchment to the

point of use so that if one control measure is insufficient, other control measures are in place to

minimize the risks to the safety of the water supply.

• WSPs should not be considered additional work; they provide a new way to do work more efficiently

and effectively.

• There are five stages of a WSP (Figure 0.1):

1. Preparation

2. System assessment

3. Monitoring

4. Management and communication

5. Feedback

• The WHO/IWA WSP manual describes a modular 11-step approach, on which this training package is

based (Figure 0.1).

Benefits

• A key benefit of WSPs is that utility staff become more aware of their role in the provision of safe

drinking-water.

• Other benefits may include cost savings (e.g. by reducing or eliminating any unnecessary monitoring

and testing, reducing the need for treatment or improving maintenance), improved communication/

stakeholder relationships and management and operation of the utility.

5

__________________________________________________________________________________________

Why are traditional ways of ensuring water safety not enough?

__________________________________________________________________________________________

Read through the London cholera case-study. Discuss points of interest.

London – 1854 In the 19th century, London was the largest city in the world, with serious overcrowding issues.

The Soho district had serious sanitation problems. There was no sewerage system, and most properties had

cesspools beneath their cellars that were overflowing. The government decided to dump this waste into the

River Thames, which contaminated the drinking-water supply and led to a number of cholera outbreaks. A

physician, John Snow, with the help of the Reverend Henry Whitehead, made the connection between these

outbreaks and a contaminated water supply.

On 31 August, a major cholera outbreak affected Soho. Over the next three days, 127 people near Broad

Street, Soho, died. The following week, three quarters of the residents had fled the area. By 10 September,

500 people had died, and the mortality rate was 13% in some areas of the city. By the end of the outbreak, 616

people had died.

The dominant theory at the time was that diseases such as cholera were caused by air pollution. This

unfortunately spurred on the practice of dumping raw sewage from cesspools into the Thames, in order to

“clean” the air around living areas. At the time, the germ theory was not widely accepted. John Snow believed

that cholera was spread via the water.

By talking to local residents, he identified the source of the outbreak as the public water pump on Broad

Street. Although Snow’s chemical and microscopic examination of the water was not able to prove its danger,

his studies of the pattern of disease were convincing enough to persuade the local council to disable the

pump.

Snow used a spot map to illustrate how cases of cholera were centred around the pump. It was discovered

later that this Broad Street pump well had been dug only three feet from an old cesspit and was being

contaminated from a domestic sewer pipe. He used statistics to illustrate the connection between the quality

of the source water and cholera cases.

Despite Snow’s efforts, it was not until 1858, when the stench of the polluted Thames was unbearable, that

the germ theory of disease was considered. Parliament sanctioned one of the century’s great engineering

projects – a new sewer network for London, which opened in 1865.

6

Exercise – Introductory module

Aim: To reinforce the public health role of suppliers and remind participants of what the potential health

impacts would be within the population if treatment were to fail or were insufficient to remove such

contamination, thus highlighting the need for an effective WSP

Timing: 15 minutes

Structure: Groups of four

Feedback: Swap tables and mark other group’s work

Complete the missing sections of Table 0.1 using the possible answers below. Complete the laminated table

provided. After 15 minutes, you will be asked to swap tables with another group to mark each other’s work.

Possible answers:

• Lead

• Escherichia coli

• Dysentery

• Faecal contamination

• Diarrhoea and intestinal malabsorption

• Occurs naturally, grows well at high temperatures

• Legionella pneumophila

• Too much: adverse changes in bone structure

• Cryptosporidium parvum

• Liver damage, neurotoxicity and possibly tumour promotion

• Cholera (severe diarrhoeal disease)

• Addition during treatment and naturally in the environment

• Skin changes and cancers of the skin, lung and bladder (after long term exposure)

• Occurs naturally and in certain human-made installations such as water cooling devices and spas

• Faecal contamination

__________________________________________________________________________________________

_______________________________________________________________________________________

7

Table 0.1 – Incomplete table of parameters and their impact on health

Parameter Potential health impact Potential source (in water)

Diarrhoea

Faecal contamination (indicator

for faecal contamination)

Shigella spp.

Vibrio cholerae

Diarrhoea Faecal contamination

Giardia intestinalis

Faecal contamination (wide range

of animal species)

Naegleria fowleri

Amoebic meningitis (via

inhalation)

Pneumonia (via inhalation)

Fluoride

Arsenic

Adverse neurological effects Old pipes and plumbing

Cyanobacterial toxins Bacterial blooms in raw water

8

Module 1 – Assemble the WSP team

Learning objectives

Through active participation in and successful completion of Module 1, each participant should be able to

meet the following learning objectives:

• Demonstrate clear understanding of the purpose of the WSP team and therefore who should be

involved in WSP development and implementation.

• Explain why engagement of senior management from the outset is of vital importance.

• Evaluate the relative importance of all WSP stakeholders with regard to ensuring the delivery of safe

drinking-water.

• Identify the expertise needed to design and implement an effective WSP with clearly assigned roles.

Key points

• A WSP team should be formed to own and lead WSP development and implementation efforts and to

advocate the approach to those connected with the safety of the water supply.

• A WSP team is largely made up of people from within the water utility, but, if required, external

stakeholders and consultants may be approached for their expertise. Any requirement for new staff or

external advisory input should be identified early on.

• In order for WSPs to be implemented successfully, senior management buy-in is needed from the

outset to support changes in work practices and provide financial and resource support.

• A team leader needs to be appointed to ensure focus.

• Members of the team must have appropriate authority to implement recommendations that result

from the WSP.

• Team members must be skilled in risk management and collectively have knowledge of the entire

supply chain. It is essential that the expertise needed is matched to a person responsible and that all

roles are clearly defined.

• Key members will vary according to the context, but will likely include in-house operators, engineers,

scientists, risk managers, technicians, external regulators, environmental agencies and landowners.

• Information about the WSP team members (e.g. name, job title, role within the WSP team and contact

details) must be recorded and updated as necessary (see Table 1.1).

• The size of the team should depend on the size of the organization and complexity of the system (a

small team is better than no team). For further information, see example/tool 1.3 in the WSP manual.

• The initial time input for WSP development and implementation may be high, but it will decrease over

time as the WSP team becomes more familiar with the WSP process.

• Team development poses a number of challenges: finding skilled personnel, organizing the workload,

identifying and engaging external stakeholders, keeping the team together and effective

communication.

__________________________________________________________________________________________

9

Table 1.1 – WSP team details form

Why should you assemble a team?

__________________________________________________________________________________________

Why do we need to engage senior management?

__________________________________________________________________________________________

Are there any additional external support resources you could engage?

__________________________________________________________________________________________

How could you overcome the challenges presented?

__________________________________________________________________________________________

The main outputs from Module 1 will be the establishment of a multidisciplinary team that understands the

supply system, is well placed to assess the risks associated with the system and has authority to implement

recommendations resulting from a WSP.

10

Exercise – Module 1

Aim: To identify key competencies required for WSP teams and create a list of potential contacts

Timing: 25 minutes

Structure: Groups of four

Feedback: Groups verbally provide feedback to workshop

Group together with other members of the same utility (if there are only single participants from each utility,

then groups may discuss together, but prepare individual lists). List an ”ideal” WSP team from within your

utility. On a flipchart, write down job titles and names if you know them, the expertise they will bring to the

team, contact information and back-up contact details. Identify what expertise is missing, and make

suggestions of who you could ask to help source this expertise. Are there any external stakeholders that

should be approached?

Nominate a rapporteur and someone to provide feedback to the main group at the end of the exercise. Lists

produced can be taken back and used as a starting point for recruiting potential WSP team members.

__________________________________________________________________________________________

11

Module 2 – Describe the water supply system

Learning objectives

Through active participation in and successful completion of Module 2, each participant should be able to

meet the following learning objectives:

• Identify what factors need to be considered when describing a water supply system.

• Design and construct an interlinked flow diagram of system components (from source to point of use)

for a known system.

• Formulate a list of common challenges encountered when describing a system.

Key points

• It is necessary to describe each supply system in order for subsequent risk assessments to be carried

out with confidence.

• The entire system (from catchment to point of use) needs to be described, with the final uses and users

identified. These should also explicitly state what and who the water is not suitable for.

• The supply system should be described relative to the water quality standards required, which are

based on the local health-based targets.

• Site visits as well as document analysis will be required for an effective description.

• Descriptions (module outputs) will include personnel, system flow diagram, water quality information

(treated and untreated) and expected deviations due to changes in weather conditions.

__________________________________________________________________________________________

Items to include in a water supply system description

Catchment: _________________________________________________________________________

__________________________________________________________________________

Treatment: __________________________________________________________________________

__________________________________________________________________________

Distribution: __________________________________________________________________________

__________________________________________________________________________

User: __________________________________________________________________________

__________________________________________________________________________

12

What areas of the system do utilities not have direct control over? For these components, what activities can

utilities partake in, to support water safety?

________________________________________________________________________________________

Typical parameters that may be measured with regard to water quality include:

________________________________________________________________________________________

Possible challenges that might be faced when describing a supply system:

________________________________________________________________________________________

The main output from Module 2 will be a detailed, up-to-date description of the water supply system that

includes a system flow diagram, water quality information (treated and untreated), expected deviations in

source water quality due to changes in weather conditions, an identification of the uses and users of water and

availability of trained staff.

13

Exercise – Module 2

Aim: To describe a known water supply system and document as a flow diagram

Timing: 25 minutes

Structure: Groups of four

Feedback: Swap tables and review another group’s flow diagram, and provide feedback to the workshop after

the exercise

Create a basic flow diagram of a water supply system known to you or a member of your group. Use the

symbols (shown below) to define each step. The system should be described from catchment to point of use,

with notes made (star) where the system is unknown/not known in sufficient detail. In these situations, you

should identify how this information will be obtained, including identification of relevant stakeholders to

provide this information.

To supplement the flow diagram, reference should be made to other documentation (banner symbol) that

would provide more information, e.g. treatment works process flow diagram.

Circle = Operational step

Triangle = Storage step

Block arrow = Transport step

Star = Unknown part of system

Banner = Refer to other documentation

Dashed line arrow = Intermittent process

Full line arrow = Continuous process

BOLD/Blue

Bold/Blue = Utility control

UNBOLD/Red Non-bold/Red = Outside of utility control

__________________________________________________________________________________________

14

Module 3 – Identify hazards and hazardous events and assess the risks

Learning objectives

Through active participation in and successful completion of Module 3, each participant should be able to

meet the following learning objectives:

• Explain the stages and meaning of hazard identification and risk assessment.

• Undertake risk assessments of given hazards/hazardous events.

• Identify vulnerable areas or processes in a water supply system.

• Outline the common challenges associated with the use of risk assessment methods.

Key points

• In practical terms, Module 3 is carried out concurrently with Modules 4 and 5 and forms part of the

system assessment.

• Definitions:

o Hazard – any agent (physical, chemical, biological or radiological) that can cause harm to public

health.

o Hazardous event – any process that introduces hazards to, or fails to remove them from, the

water supply.

o Risk – the likelihood of identified hazards causing harm to exposed populations in a specific time

frame and the magnitude and/or consequences of that harm.

• The first component of Module 3 is to identify potential hazards and hazardous events and then to

assess their risk.

• Identifying hazards and assessing risks will likely involve site visits, but should also be carried out by

reviewing the system description (including the flow diagram), historical data and predictive

information.

• Risks can be assessed either quantitatively or qualitatively. For example:

____________________________________________________________________________________

• It is essential that the risk matrix used is tailored to the local context. For example, detailed definitions

for the severity and likelihood categories should be developed based on the local context. The risk

matrix score that identifies significant risks should also be defined. There is no one way to conduct the

risk assessment. Regardless of the methodology that is adopted, it is important to be consistent in the

assessment approach (e.g. the likelihood and severity scoring criteria) to enable meaningful

prioritization of the risks.

__________________________________________________________________________________________

15

What are some generic hazards found within each stage of a water supply system?

Catchment: __________________________________________________________________________

___________________________________________________________________________

Treatment: ___________________________________________________________________________

___________________________________________________________________________

Distribution: ___________________________________________________________________________

___________________________________________________________________________

User: ___________________________________________________________________________

___________________________________________________________________________

How would you be able to determine what might go wrong with the water supply system?

__________________________________________________________________________________________

Algal blooms in reservoir – example risk score

In your groups, assess the risk of algal blooms and designate a score. Remember to record the rationale for the

risk assessment score.

__________________________________________________________________________________________

The Module 3 outputs are essentially to describe what could go wrong and where and to assign a risk score.

16

Exercise – Module 3

Aim: To assign raw risk scores for three given hazardous events and appreciate how difficult it is to be

consistent in such assessments

Timing: 25 minutes

Structure: Groups of four

Feedback: Verbal feedback to workshop after exercise

Identify the hazard and hazardous event and assess the risks for the three given examples, assigning a raw risk

score. Note how and why you came to that score and be prepared to feed back this rationale to the workshop

after completing the exercise. An example risk assessment matrix is shown in Figure 3.1. Answers should be

recorded on a flipchart; refer to the examples for guidance.

Note: Summary handouts of the case-studies from which these hazardous event examples are taken are

available from the facilitator on completion of the exercise.

Hazardous event 1 – Score the raw risk of microbial pathogens not being removed from the source water due

to failure of a chlorine dosing pump using the risk matrix provided.

Hazardous event 2 – Score the raw risk of water main breaks and ingress of pathogens and soil into water

mains during repair using the risk matrix provided.

Example 1

Chlorine dosing pump breaks down at a chlorination-only treatment facility. Based

on records, this occurs once every two weeks. Untreated water enters the water

distribution system and reaches some customers.

Hazardous event Brief description of the hazardous event

Hazard What is the hazard?

Likelihood of

hazardous event

If there are no controls in place, what is the likelihood of contamination during a

dosing pump failure? What is the rationale for the likelihood score?

Severity or

consequence

What is the severity or consequence if pathogens enter the water distribution system

and reach the customers? What is the rationale for the severity score?

Raw risk score Calculate the raw risk score based on the likelihood and severity ratings.

Example 2 Water main breaks (bursts) at least once a week in a distribution system. A work

crew attends the burst site, repairs the main and restores the water supply.

Hazardous event Brief description of the hazardous event

Hazard What are the hazards?

Likelihood of

hazardous event

If there are no controls in place, what is the likelihood of contamination of the water

distribution system due to the repair works? What is the rationale for the likelihood

score?

Severity or

consequence

What is the severity or consequence if pathogens enter the water distribution system

and reach the customers? What is the rationale for the severity score?

Raw risk score Calculate the raw risk score based on the likelihood and severity ratings.

17

Figure 3.1 – Example semiquantitative risk assessment matrix

18

Module 4 – Determine and validate control measures, reassess and prioritize the risks

Learning objectives

Through active participation in and successful completion of Module 4, each participant should be able to

meet the following learning objectives:

• Understand the terms control measure and validation.

• Identify typical control measures for all stages of a water supply system.

• In given examples, assess which measures are used to control certain hazards.

• Explain the processes involved in validating control measures.

• Discuss the challenges of prioritizing risks.

Key points

• In practical terms, Module 4 is carried out concurrently with Modules 3 and 5 and forms part of the

system assessment.

• Module 4 contains four stages:

• Definitions:

o Control measure – any action or activity that can be used to prevent, eliminate or reduce to an

acceptable level any water safety hazard

o Validation – investigative activity to identify the effectiveness of control measures. It provides the

evidence that elements of the WSP can effectively meet the water quality targets.

• Validation (assessing effectiveness) is the process of obtaining evidence on the performance of control

measures. It may require an intensive programme of monitoring during normal and exceptional

operating conditions.

•

The effectiveness of control measures should be based on long-term average performance and should

inform where controls are substandard. The risks should be recalculated with a consideration of existing

control measures and their effectiveness.

•

Major challenges include:

o Assessing control measure effectiveness (validation)

o Uncertainty in prioritizing risks due to lack of knowledge and/or data to assess risks

o Inconsistent risk assessment methodologies.

__________________________________________________________________________________________

Identify

control

measures

Assess

effectiveness

Reassess

risks

Prioritize

risks

19

List of common control measures found in a water supply system