Water sanitation hygiene

Quantitative microbial risk assessment

Application for water safety management
Updated November 2016

World Health Organization

Quantitative microbial risk assessment

Publication details

Number of pages: 204
Publication date: 2016
Languages: English
ISBN: 978 92 4 156537 0


The World Health Organization’s (WHO) water quality guidelines recommend a preventive, risk-based approach to water quality management from source to exposure for the management of microbial hazards. Risk assessment therefore plays a central role in implementing the guidelines as a critical component of water safety plans and sanitation safety plans. Several risk assessment approaches are available, ranging from risk scoring in sanitary inspections and risk matrices to quantitative microbial risk assessment (QMRA).

For the first time, WHO synthesizes the current knowledge on QMRA to facilitate its application in the practice of water supply, water reuse and water recreation to support the management of risks associated with faecal pathogens in the waterrelated context. A four-step QMRA framework harmonized across the water supply, reuse and recreation contexts is presented, and the value of QMRA for water safety management is described.

Guidance is provided to support the successful implementation of QMRA. Key aspects include: the role of interaction between risk managers and risk assessors; interpretation of scientific data including uncertainty; and interpretation of quantitative results. Many examples including six full case studies are described.