Cross-Connection & Backflow Control Program

To protect the City’s drinking water distribution system, the City of Modesto initiated the Cross-Connection and Backflow Control Program.


Water distribution systems are designed to distribute water to residences and businesses, with water flowing away from the supply. Backflow occurs when the water flows back to the supply, contaminating the clean water supply.

One of the most common causes is when one section of piping loses pressure. This creates a siphon, drawing water from an unknown source in the opposite direction back to the clean water supply. Another cause can be attaching a higher pressure device to the water supply, common for industrial customers.

Backflow Control Program

The City of Modesto recognized this threat to health and initiated the Backflow Control Program (BCP) to limit the risk of backflow.

All commercial and industrial businesses in the City must have a backflow prevention assembly. These devices allow water to travel in only one direction to protect our drinking water supply.

The BCP keeps a record of all devices throughout the City. Owners must have the devices tested each year by a certified tester to ensure they are working properly, and the results must be reported to the City.

If a backflow prevention assembly is not working properly, it must be repaired. Failure to do so is a public health risk and may result in fines and an interruption in water services.

Commercial Backflow Preventer
Small Backflow preventer