What is a Cross-Connection?
A cross-connection is any connection between your drinking water and any other source of
water that combines the two when a backflow condition occurs; typically resulting in contamination
of the water system.
What is a backflow?
Backflow occurs when the water in your pipes (after the water meter, in your building/facility)
goes backward (opposite its normal direction). There are two situations that can cause the water
to go backward (backflow):
- Backpressure – when the pressure in your pipes is greater than the pressure coming in.
- Back-siphonage – when there is a reduction of pressure in the water distribution system
Safe Drinking Water Act
In 1974, the Safe Drinking Water Act (SDWA) was established to protect human health from contaminants
in drinking water and to prevent the contamination of existing groundwater supplies. This act and its
amendments (1986 and 1996) require many actions to protect drinking water and its sources. One of these
actions is the installation and maintenance of an approved backflow prevention assembly at the water service
point of connection. These devices are installed whenever a potential hazard can exist in a given system as
the backflow prevention assembly prevents a cross-connection.
To protect the water system, there are two types of backflow prevention assembly devices that prevent the
backflow of water. These are required for all customers (typically business/industrial) to prevent a potential
hazard from entering the City’s water system:
- External – to protect the City’s water system from cross-connection occurring on the customer’s
- Internal – to protect the customer from cross-connections occurring within the system/pipes on their
To keep your drinking water safe, the City’s Cross-Connection specialist diligently checks the plans of each
new business for compliance with cross-connection/backflow requirements. When a property is renovated, a backflow
assembly may be required. Per the City’s Municipal Code, each unit must be tested annually at the expense of the
The City of Modesto takes pride in the quality of drinking water provided to our customers. To ensure the highest
water quality, distribution systems are tested weekly and quality is maintained by ensuring protections at the water
meter/point of connection, with an approved backflow prevention device.
How Can You Help?
- Be aware of potential cross-connections in your water supply and eliminate them.
- Install backflow prevention assemblies where appropriate.
- Repair and replace your backflow assembly when necessary.
- All backflow prevention assemblies are to be tested annually at the owner’s expense. (Modesto Municipal
Code 11-1.113 and California Health and Safety Code 116800-116820.) If you would like to view a list of
certified testers click here.
The Cross-Connection specialist is available to help conduct a backflow survey within your facility to determine
what type of backflow prevention assembly is best to protect your facility and your personnel. You will receive a
survey report complete with recommendations. To arrange for this free service, you may contact us at