What is the purpose of a hose bib vacuum breaker?

The purpose of a hose bib vacuum breaker is to prevent backflow from garden hoses into the potable water supply. This device is designed to protect the drinking water system from contamination by ensuring that any water that might be siphoned back into the supply does not carry with it potential harmful substances, such as pesticides or fertilizers that are commonly used in gardening and landscaping.

When water pressure drops—such as when a hose is in use and the tap is turned off—the vacuum breaker allows air to enter the system instead of allowing the potentially contaminated water in the hose to flow back into the clean water supply. This is a crucial safety feature in plumbing systems, especially in residential settings where hoses often come into direct contact with soil and chemicals.