Backflow is the undesirable reverse flow of non-potable (non-drinkable) water or other substances that can contaminate the drinking or public water system due to a cross connection in the piping. Preventing backflows is important for protecting drinking water quality.

Austin Water administers a backflow prevention program in conjunction with federal, state and local codes to ensure backflow prevention devices are installed and maintained where backflow may be a risk.

How Backflows Happen

Water delivery relies on pressure; it always takes the path of least resistance as it travels through the water system from high to low pressure areas. Normally, water travels in one direction, from treatment plants, through water mains, then to each customer’s service connection. Certain pressure loss incidents, such as a water main break or fully opened fire hydrant, can force water back into the drinking water system.

Customer water can be exposed to chemicals, microbes and other harmful substances through sinks, irrigation systems, toilets, showers, washing machines, hose bibs, or through commercial fixtures including boilers and cooling towers. Some appliances have built-in backflow prevention for this reason, but many do not.  Potential contamination can make extra protection necessary for landscape irrigation systems, spas, swimming pools, solar water heating systems, or even a bucket of soapy water being filled by a garden hose.

Backflow Types

Backpressure backflow caused by downstream pressure that exceeds the upstream supply pressure in the drinking or public water systems due to a high pressure source. This could be caused by pumps, boilers or storage tanks.

Back-siphonage backflow caused by a negative pressure (i.e., a vacuum or partial vacuum) in the drinking or public water system. It can occur when water use exceeds normal delivery capacity of the water supply (e.g., a nearby fire fighting or a water main or service pipe break).

Backflow Prevention Assemblies

Typically, backflow prevention assemblies are required for plumbing system connections that contain industrial fluids or chemicals, irrigation systems, fertilizers, or auxiliary water sources (including reclaimed water). These devices are subject to annual inspection, maintenance, testing and reporting requirements to ensure each device continues to protect against cross connections. Backflow prevention assembly requirements are determined by plumbing inspections performed at initial or remodel construction projects during the Building Permit Process.

For more information on backflow prevention: