Nitrate
Where does it come from?
Nitrate is present in all tap and bottled waters. It is produced during the natural decay of vegetable material in soil. Rainfall washes nitrate from sub-soil into groundwater. Nitrogenous fertilisers used on arable farmland can be a significant source of nitrate in groundwater and surface water.
Why is it necessary to control nitrate in water?
High concentrations of nitrate in water can cause methaemoglobinaemia (blue baby syndrome) in very young children. This is a potentially fatal illness. Nitrate is converted to nitrite in the gut and interferes with the absorption of oxygen by the blood. This extremely unusual illness only occurs at very high nitrate concentrations. The last recorded case in the UK occurred in the 1950s and was associated with the use of a shallow private well. No cases have arisen from use of public water supplies.
The current regulatory standard of 50 mg/l nitrate is derived from the standard in the European Union's Drinking Water Directive. The EU standard is based on the World Health Organisation's guideline value for drinking water, which is also 50 mg/l. That standard is intended to ensure that drinking water will not cause methaemoglobinaemia.
What about Nitrate and cancer?
A number of studies have demonstrated that extremely high doses of nitrate can cause cancer in laboratory animals. A number of epidemiological studies have investigated the possible association of nitrate in tap water and incidence of cancer. None have provided any evidence for an association. Indeed several have reported an inverse association i.e. cancer incidence decreased as the nitrate levels in water increased. It is important to note that nitrate is a natural component of many foods including green vegetables and that food provides the highest proportion of our dietary nitrate intake.
How much nitrate is in your water?
In 1999, 99.94% of tests for nitrate on samples taken from public water supplies in England and Wales met the nitrate standard. Remedial action is being taken in the few locations where the standard is exceeded. This action involves installation of treatment processes to reduce nitrate concentrations. Alternatively, blending of high nitrate water with water that is low in nitrate is practised to achieve compliance with the nitrate standard.
Summary statistics on nitrate concentrations in all water company areas are included in the Chief Inspector's Annual Report, which can be found on this website. Consumers can obtain specific information about nitrate concentrations in their tap water from their local water company. Contact details are given on the water bill or in the local telephone directory.
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Updated 11 July 2001
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