Report No DWI0138


(SD 3423) Final Report to the Department of the Environment DoE 3305/4


Aug 1993


Due to the lack of information on the frequency and effect of backflow events in water systems the Department of the Environment contracted WRc to carry out a study of the feasibility of undertaking a major survey. The purpose of this study was to ascertain if a major survey was necessary and what the scope, cost and benefit of such a survey would be. This contract was carried out under the supervision of the Drinking Water Inspectorate.

The 1974 report to the DoE Committee on Backsiphonage in Water Installations concluded that the majority of recorded events were at industrial plants and were mostly due to cross connections. The report recommended that all systems should be brought up to standard within five years; the 1986 bye-laws provided the legal framework to prevent backflow in potable water systems.

In the present study a detailed questionnaire on backflow events was sent to water undertakers in England, Wales and Scotland. Those undertakers who provided evidence of proven events were subsequently visited to assess the quality of their records. Considerable variation was found in the quality, format and extent of the records maintained.

Of the 78 proven events recorded in the study, the majority (53%) had occurred at industrial or business premises. The number of reported events showed a reduction when compared to the 1974 situation. Problems with the installation of combination boilers accounted for 39% of the reported domestic backflow events. A survey of the literature showed the UK experienced similar problems to those reported overseas.

The feasibility study recommends that a major study of backflow events should not be undertaken. It also stated that water undertakers should bring to the attention of their customers, the responsibility of individuals for the correct installation, main tenance and operation of their apparatus (Section 73 of the Water Industry Act 1991). A further recommendation is that the water undertakers should arrange for a plate to be attached to combination boilers advising of the correct procedure for primary circuit filling. They should also advise consumers of the risk and prevention of backflow.

Copies of this report may be available as an Acrobat pdf download under the 'Find Completed Research' heading on the DWI website.