asked the Secretary of State for the Environment if he will list in the Official Report which substances other than H2O are present in London water supplies, and in what normal proportion. and stating which are introduced artificially and for what purposes; and whether any other substances are introduced into any water supplies in any other part of the country, and for what purposes.
A very large number of substances can be present in drinking water in trace amounts. I shall write to the hon. Member with details.In the London area the only chemical additives used are chlorine to destroy pathogenic bacteria, sulphur dioxide to remove excess chlorine, and in a few instances amonia to produce chloramines. In other parts of the country, the following other additives are also sometimes used: chlorine dioxide and ozone as substitutes for chlorine, lime or sodium hydroxide to correct acidity, calgon— sodium hexame taphosphate—to inhibit corrosion and fluorides. Coagulants and floculants used in the treatment process are removed before the water is put into public supply.
asked the Secretary of State for the Environment what is the proportion of fluoride in the water supply at Twickenham.
The natural fluoride levels in water vary from time to time. I understand that the average level in Twickenham's public water supply last year was 0·2 mg/1. No fluoride is added by the water authority.