Backflow is a term in plumbing for an unwanted flow of water in the reverse direction.
Backflow can be a serious health risk if the mains water supply is comes into contact with foul, stagnant or contaminated water.
In the most obvious case, a toilet flush cistern and its water supply must be isolated from the toilet bowl. For this reason, the Water Supply (Water Fittings) Regulations 1999 require installers to undertake a series of safety measures and install backflow prevention devices.
Causes of backflow
Backflow can occur when the mains pressure becomes lower than the pressure in the supply pipe.
- Incorrectly installed plumbing systems
- Burst mains
- Pumps on supply pipes
- Using hydrants for firefighting
- Install a storage cistern to 'break' the mains supply at a float operated valve
- Install mechanical backflow preventers, such as non-return valves
- Ensure physical air gaps are maintained at taps and top-up pipes