Richard Bateman, Product Marketing Manager at RWC, explains why reduced pressure zone valves are essential for preventing backflow in commercial and public use buildings.

Clean and safe water supply is the backbone for any type of a building and plays a critical role in keeping it up and running. Therefore, adequate protection against backflow is crucial in commercial buildings to ensure undisrupted operations and to keep the mains water supply free from contaminants.

In this article we will discuss what backflow is, where in commercial and public buildings it can happen, and how to prevent it.

Understanding backflow

In most modern plumbing installations, the mains water supply is maintained at a high pressure, so showers and other water outlets run effectively. A sudden drop in pressure can cause a vacuum effect in the water supply, which can siphon stagnant water back into other parts of the system. This is known as backflow or back-siphonage.

The other cause of backflow is back-pressure. This can happen when a system is operating under higher pressure than the pressure within the water mains. An example of this is when increased pressure builds up in an unvented hot water cylinder, due to the expansion of water when it is heated. Without adequate protection, this could result in a ‘crossflow’ effect, which could push the water down the cold supply feeding it.

The dangers of backflow

Backflow in commercial buildings can happen from a number of sources, including external hosepipes, washing machines, dishwashers, baths, showers, and even swimming pools. Wastewater from these sources will carry anything from micro-organisms to cleaning chemicals, all of which can contaminate the mains water supply, making it unfit for use.

If backflow happens in a commercial setting, like schools, hospitals, and hotels, it can have a wide impact on the operations of these buildings and the neighbouring communities, as the mains water supply will need to be drained and cleaned to ensure it’s safe for consumption.

Reducing the risk of backflow

To adequately protect the water systems, installers must know what backflow prevention devices are needed, and that depends on the identified fluid risk present in a building.

There are five fluid categories as defined in the Water Supply (Water Fittings) Regulations (1999) for England and Wales, with Fluid Category 1 posing the least danger and Fluid Category 5 posing the maximum risk.

In commercial buildings with applications deemed a Fluid Category 4 risk to the mains supply, reduced pressure zone (RPZ) valves are often the preferred solution. Other backflow prevention devices are required if the usage or an appliance is deemed a Fluid Category 5 risk.

RPZ valves are intended to prevent any contaminants from entering wholesome water within the building or the water mains, and should be installed, commissioned, tested, and maintained by an approved RPZ Valve Tester.

Backflow prevention devices in commercial settings also need to be regularly serviced to ensure optimum performance. In the case of RPZ valves they must be tested at least annually or as specified by the local water undertaker. This is where having a safe and reliable solution is vital.

Retrofit projects

In addition to new installations, it is crucial to check that water systems in refurbished commercial properties are also adequately protected against backflow. It is even more important to check for RPZ valves in properties built prior to 1999, as they were built before the Water Supply (Water Fittings) Regulations or Byelaws in Scotland were implemented. But retrofitting heritage buildings comes with its own set of challenges, with many of them only giving minimal space to work in.

Regular maintenance

Once RPZ valves have been installed, they must be tested, and the installer must notify the water authorities regarding the status of the works that have been carried out. As outlined in the “Water Undertakers’ Approved Installation Method” (AIM) Document, published on the WRAS website, it is essential the valve is tested every year to ensure that it is in good working order.

As discussed, some commercial applications, dependant on the type of usage, could potentially be classed as a Fluid Category 4 risk. If water from these establishments backflow into the mains water supply, they pose a public health risk and companies face the risk of prosecution. This also results in huge amounts of water being wasted when the reservoirs are drained and cleaned. So, it is essential that RPZ valves are installed and regularly serviced to keep the water network safe and clean.