Why doeyou need an anti syphon valve on outdoor hose bib?

An anti-siphon valve is essential on outdoor hose bibs to prevent backflow contamination of the potable water supply. It ensures that water cannot flow backward from the hose or any attached device into the main water line, which could introduce pollutants or chemicals. This valve helps maintain water safety and complies with Plumbing codes, protecting public health and the quality of the water supply.