Bushey Heath, United Kingdom




Well water


Potable water production


Clay Lane Water Treatment Works


160.000 m³/d (42.27 MGD)


Pentair was selected to install an ultrafiltration membrane plant to provide a barrier against cryptosporidium at the Clay Lane Water Treatment Works (WTW). Site issues led to the design of a system providing a water yield in excess of 99.95% allowing the wastewater discharge of the membrane plant to comply with current site discharge permits. Clay Lane WTW is a strategic works supplying water to the North London area. With ozonation, GAC filtration and chlorination, the site is vulnerable during periods of heavy rainfall to increases in turbidity.
Following a feasibility study comparing full water treatment against membrane filtration, Three Valleys Water opted for an ultrafiltration cryptosporidium barrier from Pentair. The solution offered was developed in partnership with Three Valleys water, OTVB and VWP (formerly GUP) and was unique in overcoming all of the site specific issues at Clay Lane together with being fully compliant to current Drinking Water Inspectorate requirements.


Prior to the ultrafiltration plant, the well water abstracted from several boreholes is treated by means of ozonation and granular activated carbon. The waterpasses through pre-filters and then through two stages of ultrafiltration prior to chlorination and discharge to the treated water storage tank on site.

Integrity testing 
In order to ensure adequate protection against cryptosporidium and full compliance with the DWI requirements for integrity testing, Pentair X-Flow has developed a number of techniques that when used together provide a failsafe solution, ensuring that the required removal efficiency is always met.

The first method is the level one Airflow Test which can identify a broken fibre within a unit. This test is fully automated and can be initiated and monitored remotely and is an order of magnitude more sensitive than traditional pressure hold tests.

To identify the vessel that holds the compromised fiber the leve two airflow test is used. The operator can choose to repair the fiber directly or isolate the pressure vessel after which the unit can be returned safely into operation.

scope of supply

Primary system

1536 x Xiga 40 UF membrane
32 x Xiga skid
Secondary system

96 x Xiga 40 UF membrane
4 x Xiga skid