Final answer:
The best method to prevent back siphoning in potable water systems is using Reduced pressure zone (RPZ) valves, which are fail-safe devices designed to stop backflow through a system of checks and balances.
Step-by-step explanation:
Back siphoning, also known as backflow, is a critical issue when it comes to maintaining the purity of potable water systems. This phenomenon can cause waste water to contaminate clean water, creating a health hazard. To prevent this, several methods are used in water supply systems:
- Air Gaps: This is a simple and effective way to maintain a physical separation between the end of a water supply outlet and the flood level of a fixture.
- Check valves: Designed to allow water to flow in only one direction, hence preventing any reverse flow.
- Vacuum breakers: These are devices that prevent back siphonage by allowing air to enter the water system if a vacuum occurs.
- Reduced pressure zone (RPZ) valves: A more sophisticated device that uses the principle of reduced pressure in a zone between two check valves to prevent backflow.
While all of these methods can be effective, RPZ valves are commonly regarded as the best solution for preventing back siphoning in a water delivery system because they provide a fail-safe barrier against both back siphonage and back pressure situations. They are especially useful in conditions where the quality of the water could cause a health hazard and where simple devices like air gaps might not be adequate.