A guide to backflow prevention and solutions to safeguard water supplies

Mother teaching her daughter to wash her hands with soap and running water. Loving mom following precautionary measures at home. Mother and daughter standing by the sink in the kitchen.

Installers are the first line of defence for maintaining the health and safety of our water supply, therefore backflow prevention is an important consideration when setting up a plumbing and heating system. Created by back siphonage, often caused by pressure failure or catastrophic pipe leaks upstream of the mains supply, backflow poses a grave risk to public health as contaminants can infiltrate the clean water supply.

Backflow risks are classified by the water regulations depending on the severity of the risk, ranging from Fluid Category 1 to 5. It is important that installers understand the different levels of risk and any corrective measures required.

Whether in domestic or commercial settings, installers play an important role in identifying the potential causes of backflow and preventing it through effective system design and maintenance. But what are the go-to solutions when dealing with backflow?

Here, we’ll answer some of the most common questions around backflow – from what causes it to how to prevent it from occurring.

What causes backflow in plumbing systems?

Backflow often occurs from a large and sudden drop in pressure. In domestic environments for example, mains water pressure is typically between 1 to 3 bar of pressure, guaranteeing the safe flow of water from taps and outlets while also protecting the supply from contamination. The challenge arises when the internal pressure drops – which could happen due to burst pipes or larger mains leaks, upstream of the property’s appliances. When this occurs, a vacuum can be created, drawing contaminated water back into the system and leading to unwanted backflow.

Backflow can occur in any plumbing system but is more common in settings such as construction sites and healthcare buildings – where the impact can be far greater. In domestic systems, external hoses or sprinkler systems equipped with fertiliser dispensers are often the culprits of the contamination, susceptible to drawing fertiliser chemicals back into the mains water supply.

Grungy image of dirty brown water running from a water stained faucet

Can backflow contamination be prevented?

Monitoring water pressure is critical in mitigating the risks of backflow, and assessing the specific risk factors within each building can determine the appropriate preventive measures. The Fluid Category levels (ranging from 1 to 5) offer installers a structured framework for understanding these risks, with level 1 posing the lowest risk and level 5 the greatest.

At lower risk levels (Categories 1 and 2), single check valves effectively safeguard against backflow. These valves allow water to flow in one direction only, preventing reverse flow and maintaining water purity. In slightly riskier environments (Category 3), double check valves offer extra protection by incorporating two check valves within the same device. Higher risk applications (Category 4) such as healthcare facilities, or even car washes that have a connection to the mains, require Reduced Pressure Zone Valves (RPZs) and must be tested annually to ensure the risk of contamination is mitigated.

Fluid Category 5 prevention is surprisingly common, where only an air break between the supply and the connected fixture is sufficient. An example is when contaminants from the toilet pan could potentially backflow into the cistern. An air gap between the cistern and the pan acts as a backflow prevention device - and is often already built into the toilet design.

By selecting the appropriate valve based on the fluid category level, installers can effectively manage water pressure to prevent leaks that can lead to backpressure, whilst mitigating the risk of contamination to the supply should a pipe break occur.

Single check or double check valves: what they are and where to use them

Single check valves effectively prevent backflow risk by enabling water to flow in one direction only, ensuring that clean water remains uncontaminated. Reliance Valves' Floguard Single Check Valves are an essential component for backflow prevention in environments rated as a level 1 or 2 contamination risk. While contamination may not pose immediate health risks, it can lead to things like foul-tasting drinking water.

For environments rated as a level 3 contamination risk and above, the use of a double check valve is recommended, such as the Floguard Double Check Valve from Reliance Valves. The function is straightforward: if one check valve fails to prevent backflow, the second check valve acts as a backup, ensuring water flow travels in one direction. These valves therefore provide an additional layer of protection against backflow. Classed as verifiable valves, they also incorporate an inspection port to monitor the check valves in the event of a blockage or failure. For a fast and simple tool-free installation, double check valves are also available in the JG Speedfit push-fit range, including options with an integrated isolation valve.  

Both Reliance Valves and JG Speedfit’s Double Check Valves offer reliable solutions for backflow prevention across a range of contamination risk levels. Whether for low-risk environments or mid-range risk settings, these valves provide effective protection against backflow, ensuring the safety and purity of drinking water. With their user-friendly features and compact design options, they offer installers a hassle-free solution for maintaining water system integrity in numerous applications.

Commercial Type BA Reduced Pressure Zone Valve

RPZ valves: what they are and where to use them

RPZ valves, the unspoken hero of backflow prevention, also play a crucial role in maintaining a safe water supply, particularly in environments where toxic substances are regularly used, such as healthcare buildings and science labs. RPZs create a physical barrier between the contaminated water source and the clean water supply, thereby ensuring maximum protection against backflow contamination.

Installation of RPZs requires the expertise of approved and competent installers due to the complex nature of the systems where they are specified – typically Fluid Category 4 and above. When selecting an RPZ valve for installation, factors such as ease of installation and maintenance should be carefully considered.

Reliance Valves’ BA RPZ Valve is a safe and reliable backflow prevention device with flat-faced union MBSP connections for easy testing and maintenance. It diverts back-fed water to a waste pipe during pressure drops or back siphonage, safeguarding the primary supply. This valve offers high-quality backflow prevention and easy installation, guaranteeing clean water supplies within commercial buildings.

From single check valves for lower-risk environments to RPZ valves for higher-risk settings, there are specific solutions available to mitigate backflow risks. By selecting the appropriate valves and taking proactive measures, installers can play a vital role in ensuring the safety and integrity of our water supply, paving the way for a safer and more efficient future.

Our family of brands

RWC and its family of brands, including Reliance Valves and JG Speedfit, offer a range of solutions for backflow prevention. For more information or for product specification advice, please visit,

Richard Bateman Headshot

Richard Bateman

Product Marketing Manager Plumbing and Heating

About the author

A highly experienced and passionate professional, I have over 15 years' experience as a commercial and domestic plumber and hold NVQ Level 3 qualifications from City and Guilds

Since joining RWC in 2015, I began as a technical engineer, utilising my extensive knowledge to provide exceptional support. Currently, I am thrilled to be working with the marketing department as a Product Marketing Manager. 

This role allows me to combine my technical background with a keen eye for market trends, ensuring that RWC's products meet the evolving needs of the industry. With my wealth of experience and commitment to excellence, I am proud to serve as a spokesperson for RWC, sharing our innovative solutions and contributing to the growth of the plumbing and heating sector.