A backflow preventer stops water from reversing direction and flowing back into the public water supply, which matters most on an irrigation system or any connection where contaminants, fertilizer, treated pool water, or standing water, could otherwise be pulled backward into the drinking water line under the wrong pressure conditions.
Florida requires annual testing of a backflow prevention device on many properties and connection types, confirming the internal check valves still seal properly rather than assuming a device installed years ago still functions the same way it did on the day it was first installed.
A failed test means a repair or a replacement of the device itself, not the surrounding irrigation or supply plumbing, and that gets scheduled and documented properly as part of the very same visit, with the paperwork handled directly.