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It is fundamental to keep potable water in water supply systems uncontaminated

It is very important to keep potable water in a water supply system uncontaminated. A cross-contamination between potentially contaminated water and public water supply systems can be prevented by

• vacuum breakers in pipe lines or hoses
• air gaps between fixtures and potentially contaminated water surfaces 

Vacuum Breakers

Backflow of potentially contaminated water to a supply system can occur due to siphoning if the pressure in the system suddenly drops to a lower level. A vacuum breaker installed in the piping or in connection with the hoses will siphon air from the surroundings when pressure drops below atmospheric pressure, preventing contaminants from entering the system.

Air Gaps

A physical separation like an air gap between a fixture and a open water surface in a sink or similar prevents contaminations entering the fixture outlet and the water supply system.

The air gap should in general be larger for larger fixtures and closed surfaces (surface with walls) than for smaller fixtures and open surfaces. It is common that

• the air gap for a fixture of size 1/2" should be at least 1" for an open surface, and at least 1 1/2" for a closed surface.
• the air gap for a fixture of size 1" should be at least 2" for an open surface, and at least 3" for a closed surface.