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The importance of ensuring WC compliance

Viega has released new Prevista pre-wall cisterns to meet updated guidelines
Specifying the right WC systems can help protect the building’s potable water supply from contamination, explains Scott James.

Innovations in bathroom and washroom systems have delivered significant benefits for users and enabled water saving. However, when specifying these products it is important to ensure they comply with the Water Supply (Water Fittings) Regulations 1999, which are intended to prevent the waste, misuse, undue consumption and contamination of the drinking water supply.

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While often not fully appreciated, the specification of good quality WC cisterns has a role in protecting the integrity of potable water supplies within a building. If poorly designed, it is possible for backflow to occur from the cistern into the supply pipework and contaminate the water.

In the past decade there have been a number of documented cases where this occurred, and the backflow was often identified because the water contained evidence of the dissolved cistern block. These became known as ‘blue water’ incidents because of the characteristic colour.

One of the simplest and most reliable ways of achieving compliance with the regulations and ensuring the system performs correctly is to specify products certified by the Water Regulations Advisory Scheme (WRAS) or Kiwa. However, the WRAS and Kiwa acceptance criteria for the design of filling valves have recently been updated to strengthen the protections against backflow and contamination of the water supply.

Pressure drops

If the valve is faulty, of poor quality or improperly installed, backflow can occur when the water level in the cistern reaches the filling valve, and a drop in pressure causes the water to be drawn back into the supply pipework. Pressure within the system may drop for a number of different reasons including leaks in the system or water being drawn from elsewhere, such as a tap, shower or toilet.

To prevent this, cisterns contain backflow protections, such as a physical air gap between the filling valve and the water level. However, in some cases these protections can become compromised or are not sufficient to prevent the backflow.
To address these issues WRAS and Kiwa updated their acceptance criteria for approval of filling valves to create a more robust requirement called the Type AUK1 air gap.

“Systems previously approved by WRAS and Kiwa may no longer comply. Product information must be reviewed carefully to make sure it meets the new guidelines.”

A Type AG air gap is a non-mechanical arrangement inside a cistern that provides a visible, unobstructed and complete physical air break between the lowest level of water discharge and the critical water level (CWL).

The physical air break must be at least 20mm, or twice the internal diameter of the inlet pipe, whichever is greater. There must also be a gap of at least 300mm from the overflow pipe to the top or spillover level of the WC pan. The overflow must be circular and of a minimum size 19mm, providing this is capable of accommodating maximum inlet flow.

Lastly there must also be at least a 15mm gap between the lowest level of the WC cistern and the top or spillover level of the WC pan.

As a result of this update, systems previously approved by WRAS and Kiwa may no longer comply. Therefore, the product information must be reviewed carefully to ensure it meets the new requirements.

At Viega, we have released new, fully WRAS and Kiwa-approved versions of our Prevista pre-wall cisterns to meet the updated guidelines. Our Prevista range, available in different heights and installation options, also includes features such as height adjustability, flexible dual flush, easy installation and simple maintenance. This allows simple compliance with the regulations, regardless of the requirements of the bathroom or washroom.

To find out more about the Viega range of pre-wall systems visit