Nitrate and private water supplies
This guidance covers the actions to be taken by local authorities in relation to a private water supply which does not comply with the nitrate standard.
For general background information on nitrate in drinking water, please refer to the Inspectorate’s nitrate guidance.
Background
In 2019 Public Health England (now superseded by the UK Health Security Agency – UKHSA) and Public Health Wales updated their advice in relation to nitrate in drinking water following new information from the World Health Organization and Health Canada concerning the potential effects of nitrate on the thyroid. If nitrate were to exceed a concentration of 50 mg/L in drinking water the total intake from the combination of drinking water and the diet could exceed the European Food Safety Authority ‘Acceptable Daily Intake’ (ADI)1 for adults. As a result, UKHSA and Public Health Wales do not recommend anyone should regularly consume water above 50 mg/L.
As before, this advice particularly applies to bottle-fed infants (up to the age of six months) and the potential acute or immediate risk of infantile methaemoglobinaemia (IM), particularly where there is also microbial contamination of the drinking water. Local authorities or individuals can get further advice and support from the UKHSA (for England) or Public Health Wales through the usual contact routes.
For supplies where one or more sample has failed the nitrate standard, local authorities are required to make an informed risk-based decision as to whether or not there is an ongoing and potential danger to health. If this is the case, the local authority must serve a regulation 18 notice in England or a regulation 20 notice in Wales. Local authorities are advised to consider the following in making risk-based judgements:
- Whether or not the nitrate concentration in the water has exceeded the standard on more than one occasion.
- The likelihood of further breaches, given the findings of a source to tap supply risk assessment.
- The minimum, maximum and average recorded concentration of nitrate in the water supply over an historic period and the associated trend.
- The potential maximum concentration of nitrate in the water supply in the future considering:
- whether the sample results available highlight an increasing trend.
- the ongoing land use in the catchment, and the connectivity between the soil and the water source.
- whether mitigation will be achieved by blending with a low nitrate source or with the installation of treatment. Please see our guidance page on chemical removal of contaminants.
- The likely future use of the water supply, for example: domestic purposes only, commercial use only, mixed commercial/domestic purposes, non-domestic use (for instance: irrigation), use for consumption at a public activity (for instance: within a public building, at a festival or show).
Should the local authority decide that the nitrate exceedances are ongoing or likely to be ongoing and therefore a potential danger to health then a regulation 18 notice in England, or a regulation 20 notice in Wales must be served. The notice should include short term measures to protect health (for example: with the provision of an alternative wholesome supply) and longer-term measures such as the installation of treatment or blending of the supply to reduce the concentration of nitrate to below 50 mg/L.
- Acceptable Daily Intake (ADI) is the estimate of the amount of a substance in food or drink, expressed on a body weight basis (e.g. mg/kg body weight/day), that can be ingested daily over a lifetime by humans without appreciable risk. ↩︎