§ Mr. SedgemoreTo ask the Secretary of State for the Environment if he will make a statement about the presence of chironomid larvae found recently in the water supply emanating from Hampton works; whether there are any dangers to health; whether any pathogenic organisms, including cryptosporidia and aeromonas, could have passed through the works; and what action the communicable disease surveillance centre has taken.
§ Mr. HowardThames Water has informed me that it is satisfied that the chironomid larvae problem is under control. Initially five filters were taken out of supply as a precaution. Three were found not to be the cause of the problem and were returned to service. One of the others was marginally affected. This was drained down, inspected and re-sanded and is shortly to go back into service. The other bed which was most affected is undergoing a thorough structural investigation and will be out of service for some time. The contact tank at the Hampton works was also taken out of use in two stages, was cleaned and is now fully operational.
Thames Water has been monitoring intensively the Hampton works and associated distribution system for pathogenic organisms including cryptosporidium. It did not detect salmonellae, entero-viruses or giardia in any of the samples. Aeromonas, an organism which can colonise slow sand filters, was detected in samples of water leaving the works and in the distribution system. It is commonly found in distribution systems and there is no evidence that when present in water supplies it is detrimental to public health.
Thames Water found that many of the samples of water from the works and the distribution system contained low levels of cryptosporidia. As a precaution the Communicable Diseases Surveillance Centre is monitoring the occurrence of human cases of cryptosporidiosis and giardiasis in the parts of London supplied by the Hampton works in order to detect any significant increase in the number of cases, should this occur. So far no such increase has been detected. Thames Water is continuing to monitor samples of the works inlet and outlet for cryptosporidia.