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The Water Supply (Water Fittings) Regulations 1999 are intended to prevent the waste, misuse, undue consumption and contamination of the drinking water supply. These regulations place a legal duty on users, owners, occupiers and anyone who installs plumbing systems, water fittings and water-using appliances to ensure they are installed and used in accordance with the regulations.

In terms of product specification, the best way to achieve this is to select products that are certified by the Water Regulations Advisory Scheme (WRAS) or KIWA. However, specifiers should be aware of recent changes to the acceptance criteria for the design of filling valves to prevent backflow and contamination of the water supply. As such, previously WRAS and KIWA approved systems may no longer comply and so it is important to look carefully at the product information to ensure it meets the new requirements.

While often not fully appreciated, the specification of good quality WC cisterns has a role to play 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 the water from toilet cisterns had been drawn back into the supply pipework and even distributed to other outlets. This backflow was often identified because the water contained evidence of the dissolved cistern block and these became known as ‘blue water’ incidents because of the characteristic colour.

Specifiers should be aware of recent changes to the acceptance criteria for the design of filling valves to prevent backflow and contamination of the water supply

Glen Peters, technical support manager, Viega

This type of backflow is caused 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, if the valve is faulty, of poor quality or improperly installed. There are a number of reasons why the pressure within the system may drop, for example 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, it was discovered that in some cases these protections had become compromised or were 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.

A Type AUK1 AG air gap definition:

• A Type AG air gap is a non-mechanical arrangement inside a cistern that provides a visible, unobstructed & complete physical air break between the lowest level of water discharge and the critical water level (CWL).
• The aforementioned 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 15mm gap between the lowest level of the WC cistern and the top or spillover level of the WC pan.

At Viega, we have released new, fully WRAS and KIWA approved versions of our Prevista pre-wall cisterns to meet the updated guidelines and these include the required Type AG air gap on the filling valves. The range consists of the Prevista Dry WC element, available in construction heights 1120, 980 and 820 mm, and Prevista Pure 3H and 3L cisterns. This allows simple compliance with the regulations regardless of the requirements of the bathroom or washroom design.

Another factor that is important to consider when selecting a WC system is water wastage. Recent reports suggest that millions of litres of water are being wasted every day due to toilet cisterns leaking water. It is estimated that where the flushing valve fails to close properly it may double a household’s daily water usage. This is also a serious issue for commercial and public buildings, where the number of WCs means the potential impact can be significant.

While there is nothing inherently wasteful about the design of the flushing ‘drop valve’ found in most WCs, their position below the waterline in the cistern means that they must seal fully to effectively prevent water escaping. There are a range of factors that can contribute to the system not operating as intended. This includes low quality valves that do not re-seat fully after activation, seals that leak or fail after a relatively short time and defects caused by poor manufacturing techniques. Therefore, it is important to ensure the chosen product has been designed and manufactured to a high standard and undergone rigorous testing.

For example, quality and longevity were a focus in the development of our Prevista cistern. To prevent any post-installation issues, it is manufactured as a single part using a blow moulding technique. This removes the need to join individual moulded components and ensures maximum leak-tightness and reliability. Each cistern is also checked for leaks and its operation tested before it leaves our factory.

Recent reports suggest that millions of litres of water are being wasted every day due to toilet cisterns leaking water. It is estimated that where the flushing valve fails to close properly it may double a household’s daily water usage.

Glen Peters, technical support manager, Viega

In addition, it is also important for building owners and occupants to understand that, like all bathroom fittings, WCs require a small amount of maintenance to ensure they continue to work correctly. This includes occasional inspection of the filling and drain valves and the removal of any debris that may have inadvertently entered the cistern. Choosing a system that provides easy access and allows the valves to be removed effortlessly will help make this simpler.

The correct choice of WC cistern is important in ensuring compliance with the water regulations, especially in terms of the integrity of potable water supplies and preventing water wastage. Our Prevista range of pre-wall systems offers a high quality, fully WRAS and KIWA approved option that also includes features such as height adjustability, flexible dual flush, easy installation and simple maintenance.

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