Most municipalities require that any actual or potential cross-connection be either eliminated or be properly protected. Backflow prevention may be required to be installed by the customer on the water service line outside the building, at one or more location within the building, or both. After the initial installation and testing of a new backflow preventer, the customer is required to have the backflow preventer tested on an annual basis to help ensure it is working to keep both the customer’s water and the public water safe from contamination.