Backflow prevention device

Such connections occur naturally in appliances such as clothes washers and dishwashers, but they must be carefully designed and installed to prevent backflow.

A closely related device is the backwater valve, which is designed to prevent sewage from backing up into a building and causing basement flooding.

An air gap is simply an open vertical space between any device that connects to a plumbing system (like a valve or faucet) and any place where contaminated water can collect or pool.

Many plumbing codes specify a minimum air gap distance required for various circumstances, such as a drain connection for a dishwasher, e.g., BS 6282.

Alternatively, a specialized backflow preventer valve may be installed at strategic locations in the plumbing system wherever there is a risk of contaminated fluids entering the water supply pipes.

[2] Where submerged mains inflow is permitted,[further explanation needed] a backflow prevention assembly is required, which protects the potable water system from contamination hazards.

approved backflow prevention assemblies are required by law, and must be installed in accordance with plumbing or building codes.