The World Health Organization (WHO) recommends two main steps in the formulation of national drinking water standards to protect health. The first is a risk assessment stage, comprising the assessment of human health risks associated with exposure to microbial or chemical contaminants. This step concludes with the formulation of guideline values for the selected contaminants. The WHO Guidelines represent this initial step. The second is a risk management stage, which translates the guidelines into appropriate national standards taking into consideration prevailing social, political and economic conditions in the country. WHO supports the establishment of less restrictive provisional standards on a temporary basis when it is clear that a country cannot meet the levels recommended in the Guidelines but, at the same time, there is need for provisional standards to serve as a means of improving drinking water quality. Such provisional standards should be made more stringent over time as national capabilities improve to implement and enforce water quality standards protective of health.