Harmonization of use of terms "risk" and "risk levels"
Rolling revision of the WHO Guidelines for Drinking-water Quality
This issue is included in the plan of work of the rolling revision of the WHO Guidelines for Drinking-water Quality.
Background
The Guidelines for Drinking-water Quality Working Group meeting (Geneva, 2004) noted that the use of the terms “risk” (which means probability of an adverse effect) and “risk levels” needs to be carefully considered and harmonized in regard to microbial, chemical and radiological risks. In particular, the difference between “best estimates” of risk as opposed to “maximum potential” risks requires clarification.
Expected end-product(s)
Revised text in chapter 8 of Guidelines for Drinking-water Quality (for second addendum) and in Policies and Procedures Manual.
Progress to date
It was agreed that the text for the Guidelines for Drinking-water Quality chapters on chemicals and radiological hazards should be harmonized to state that the risk values are not intended to indicate actual cancer cases to be expected but rather are a metric for comparing relative risks among chemicals.