Regulation 4 (Wholesomeness)
Drinking water should be wholesome, something which is defined by the three conditions of this regulation.
The first condition is that the drinking water must not contain any microorganism, parasite or substance, whether alone or in conjunction with any other substance, at a concentration or value that would constitute a potential danger to human health. This ‘catch-all’ element supplements the requirement to meet the prescribed drinking water quality standards specified in the second condition of this regulation.
The second condition refers to the strict concentrations or values for a broad range of chemical, microbiological and physical parameters, listed in part 1 of schedule 1 of the Regulations, which should not be exceeded. These prescribed standards are set to ensure drinking water is acceptable to consumers in the way it appears, its odour and taste.
The third and last condition relates to nitrate and nitrite. When found in high enough concentrations, either alone or together, these parameters can cause methaemoglobinaemia in bottle fed infants up to the age of six months and in particular those younger than three months. Whilst there are prescribed standards for each parameter, both nitrate and nitrite may occur in drinking water supplies together, so should be considered collectively by way of the nitrate/nitrite formula. This states that for the water to be not present a danger to human health, the sum of the ratio of nitrate and nitrite concentrations should not exceed one.
If all three conditions are met, then the drinking water is considered safe and wholesome. Where a supply is unwholesome AND considered to be a potential danger to human health, the local authority must act in accordance with regulation 20.
Whether or not the parameter is specified by the Regulations, there is good worldwide agreement on the science behind the setting of health and non-health based drinking water quality standards which include a wide safety margin. This expert evidence is documented by the World Health Organisation in their guidelines for drinking water quality which, along with matters of national interest, inform UK regulations.
Further advice about nitrate in private drinking water supplies can be found here.