Some may not even have it. You mention a well. If the well also provides your drinking water, then you should have a vacuum break.
Vacuum breaker. A vacuum breaker is an attachment commonly placed on a bibcock valve or toilet or urinal flush valve, that prevents water from being siphoned backward into the public drinking water system. This prevents contamination should the public drinking water system’s pressure drop.
A pressure vacuum breaker (PVB) is a type of backflow prevention device, used to keep non-potable (or contaminated) water from entering the water supply.
Shop our selection of Backflow & Vacuum Breakers in the Plumbing Department at The Home Depot.