§ Mr. Rossiasked the Secretary of State for the Environment how close to the danger level laid down by the World Health Organisation the nitrate content in the Thames and Lee rivers reached during the summer; and what steps are being taken to reduce such content.
§ Mr. Denis HowellThe World Health Organisation recommended European standard for drinking water sets an upper limit of 11.3 mg/1 nitrate nitrogen. No water which exceeded this limit was put into supply. As regards the raw water samples taken from the Thames during the summer none reached this limit, the maximum being 8.8 mg/1.
Samples of raw water taken from the Lee showed the following maxima:
June: 25 per cent. of samples exceeded 11.3 mg/I: maximum 12 mg/1.
July: 4 per cent. of samples exceeded 11.3 mg/1: maximum 116 mg/1.
August: No samples exceeded 11.3 mg/1.
September: 18 per cent. of samples exceeded 11.3 mg/1: maximum 12 mg/1.
These figures were lower than those for 1973, partly because of the successful operation of the experimental plant for denitrifying sewage effluent at Rye Meads. The Thames Water Authority has also an experimental plant at Lea Bridge for denitrifying river water after abstraction.