For a printable copy of this guidance see: Regulation-4-2.pdf (dwi.gov.uk).
Regulation 4 (Wholesomeness)
Drinking water must 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 of wholesomeness, supplements the requirement to meet the
prescribed drinking water quality standards, as specified in the second condition below.
The second condition refers to the strict concentrations or values for a broad range of chemical, microbiological and physical parameters, which are listed in part 1 of schedule 1 to the Regulations, which must not be exceeded. In addition to being protective of public health, these prescribed standards are also set to ensure
drinking water is acceptable to consumers in appearance, 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 those younger than three months. While there are prescribed standards for each parameter, this condition considers that nitrate and nitrite may occur in drinking water supplies together, and therefore need to be considered collectively by way of the nitrate/nitrite formula. This formula simply states that for the water to be considered wholesome the sum of the ratio of nitrate and nitrite concentrations to that prescribed respectively should not exceed one.
If all three conditions are met, then the drinking water is considered wholesome.
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-healthbased 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 inform the legal requirements of the EU Drinking Water Directive 1998/83/EEC from which the drinking water legislation in the UK was originally derived.
Further advice about nitrate in private drinking water supplies can be found at;
PWS regulations 2016 (as amended) v.2, September 2018