How far must public water supply lines be set back from sewer pipes with watertight joints?

The requirement for public water supply lines to be set back from sewer pipes with watertight joints is rooted in health and safety regulations to prevent contamination. A setback distance of 20 feet is deemed sufficient to ensure that there is a safe barrier between potable water supplies and potential sources of contamination, such as sewer lines.

This distance is based on considerations such as potential leakage and subsurface water movement, which can carry contaminants from sewer lines to water supply lines. The 20-foot setback is a standardized distance that balances practical installation considerations with the need to protect public health. The other distances suggested in the options might exceed the necessary minimum, leading to unnecessary costs and complexities in installation, or they may not align with regulatory guidelines established for safe public health practices.