Report No DWI0709/4

Oct 1995


The research described in this report was undertaken for DWI in advance of changes to the Water Byelaws and compares the performance of a range of WCs sourced from Europe, Australia and the US with UK products. The main objective was to establish whether or not there is any significant case for the UK to maintain its current requirements for WCs to be fitted with valveless siphonic flushing as per Byelaw 74(a).

The flushing performance of the fifteen non-UK ie non-syphonic flushing products, assessed over a variety of tests based on current UK and other national standards, was found to be as good or better that the three .7.5 litre UK products used as the benchmark. The cheaper products generally performed as well as the more expensive ones.

Endurance testing of eight flush valve products under laboratory conditions suggested that while they would all eventually leak (after 100,000 cycles or more equivalent to 10 yrs typical domestic use) the leakage rates would initially be small ie equivalent to less than one flush per week. The key determinant of water wastage would be whether the user initiated remedial maintenance within a reasonable period of time after first detecting the leakage. The same consideration would apply to leaking inlet valves, whether on siphon or valve cisterns. This test did not however simulate ageing of the flush valve seals which may be a factor in their long term performance. In most cases, seals can easily be replaced by the user without the use of tools.

Four of the tested drop valves were subject to sticking which caused serious short term leakage but in actual installations this would have been very evident to the users who would have initiated rapid remedial action, particularly if water metered. In two cases the problem was permanently corrected by minor adjustments, emphasising the importance of correct installation. In the other two cases the valve mechanism was replaced.

Overall, there is no evidence from this research that allowing the use of non-siphonic products, tested to proposed European standards and correctly installed, in the UK would have a significant adverse effect on water conservation. The small amount of leakage that ultimately occurs would almost certainly be compensated by the better performance of valved cisterns at low flush volumes.

It is, however, recommended that prior to the establishment of suitable standards acceptable to the UK, non-siphonic cisterns be permitted only where there is water metering to ensure there is a financial incentive to quickly deal with any serious leakage that may occur.

Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.