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Risk assessment

The risk assessment allows the consequence of all possible hazards from the water distribution system to be assessed, in combination with their likelihood of occurrence, so that the most significant risks can be given priority when controls are being considered.


Under section 61D (c) of the Public Health Act 2005, a water risk management plan (WRMP) must assess the risks associated with identified hazards, hazard sources and hazardous events within a facility’s water distribution system.

The risk assessment should identify:

  • differing levels of risk in different locations within the facility and
  • differing vulnerability to harm of the occupants within the facility.

It is also important to consider the type of risk when hazard controls:

  • water system risk (risk of contamination of the water distribution system) or
  • health risk (risk of a person suffering an adverse health impact from the water system).

Key steps

A cut-off or acceptable level of risk should be determined by the water risk management team for each facility before undertaking its risk assessment.

Qualitative measures of likelihood and consequence can be used to determine a level of risk. For examples of measures of likelihood and consequence, see tables 4a, 4b and 4c of the enHealth “Risk Management Plan for Legionella Control” template (see link below).

Using your water distribution system flow diagram, assess and determine a level of risk for each identified hazard and hazardous event. For example, see Table 5 from the enHealth “Risk Management Plan for Legionella Control” template.

Following the risk assessment, the level of risk for each hazard should determine whether it is within the acceptable or unacceptable level of risk, based on the pre-determined acceptable level of risk for each facility.


Last updated: 1 June 2021