Safe drinking water: the toxicologist's approach

The production of adequate and safe drinking water is a high priority issue for safeguarding the health and well-being of humans all over the world. Traditionally, microbiological quality of drinking water has been the main concern, but over the last decades the attention of the general public and health officials on the importance of chemical quality and the threat of chemical pollutants have increased with the increase of our knowledge on the hazards of chemical substances. There are many sources of contamination of drinking water. Broadly they can be divided into two categories: contaminants originating from surface and groundwater, and contaminants used or formed during the treatment and distribution of drinking water. Contaminants in surface and groundwater can range from natural substances such as arsenic and manganese leaching from soil, to contaminants introduced by human activities, such as run-off from agricultural activities, controlled discharge from sewage treatment works and industrial plants, and uncontrolled discharges or leakage from landfill sites and from chemical accidents. Disinfectants and disinfectant by-products are well known contaminants resulting from the processes used by the drinking water industry for the treatment and distribution of water. The basic question in the production of drinking water is how to rid drinking water of potentially dangerous microorganisms and chemicals without introducing new hazards that might pose new and different threats to human health. It is the responsibility of toxicologists to provide risk assessments for chemical pollutants and to derive guidelines or standards for drinking water quality below which no significant health risk is encountered, to assure consumers that drinking water is safe and can be consumed without any risk. This paper will focus on the toxicological procedures used by the World Health Organization to derive guideline values for chemical compounds in drinking water, and will touch upon some critical differences in the nature of guidelines and legally binding standards.