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IWA Water Safety Portal
Module 1
Module 2
Module 3
Module 4
Module 5
Module 6
Module 7
Module 8
Module 9
Module 10
Module 11


Module 3 Identify hazards and hazardous events and assess the risks


In practice this Module, together with Module 4 (determine and validate control measures, reassess
and prioritize the risks), and Module 5 (develop, implement and maintain an upgrade plan), are
usually carried out concurrently.

Module 3, the first step in this process, should:

• Identify all potential biological, physical and chemical hazards associated with each step in the
   drinking-water supply that can affect the safety of the water;
• Identify all hazards and hazardous events that could result in the water supply being, or becoming,
   contaminated, compromised or interrupted;
• Evaluate the risks identified at each point in the flow diagram previously prepared.

Key Actions

•Identify the hazards and hazardous events
For each step of the validated process flow diagram, the WSP team is required to assess what could
go wrong at what point in the water supply system in terms of hazards and hazardous events. 

•Assessment of risk
The risk associated with each hazard may be described by identifying the likelihood of occurrence
(e.g. certain, possible, rare) and evaluating the severity of consequences if the hazard occurred
(e.g. insignificant, major, catastrophic).  The aim should be to distinguish between significant and
less significant risks. 

Typical challenges

• The possibility of missing new hazards and hazardous events. Since risk assessment provides a
   ‘point in time’ picture of the system, the risk assessment should be reviewed on a regular basis 
   in order not to miss new hazards.
• Uncertainty in assessment of risks due to unavailability of data, poor knowledge of activities
   within the water supply chain and their relative contribution to the risk generated by the hazard
   or hazardous event.
• Properly defining likelihood and consequence with sufficient detail to avoid subjective assessments
   and to enable consistency.


1. Description of what could go wrong and where in terms of hazards and hazardous events.
2. Assessment of risks expressed in an interpretable and comparable manner, such that more significant
    risks are clearly distinguished from less significant risks.

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