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What is Cross Connection?
A driver loses control of his car and accidentally knocks over a fire hydrant. Water sprays the street, causing water pressure to drop in the entire neighborhood. In one yard, a young man washing his car has left his hose in a bucket full of soapy water. Because of the drop in water pressure, the hose sucks the bucket dry. In another home two blocks away, a child turns on the kitchen faucet to get a glass of water. The glass fills with soapy water.
This example illustrates a cross connection, which is a link between a source of pollution or contamination and the drinking water supply.
Entry of pollutants or contaminants into the drinking water supply is called a backflow. Contaminants could be soap, sewage, bacteria, insecticides, fertilizers, or other organic or inorganic substances.
Backflow is caused by back-pressure or back-siphonage. Back-pressure is when a booster pump or pressure-type chemical injector creates a pressure greater than the drinking water system, so that pollutants are injected into the water supply. Back-siphonage is when the pressure in the drink water system drops, sucking pollution back into the drinking water supply.
A backflow preventer is a device installed in a cross connection that prevents contamination of the drinking water system.
Some common cross connections that can lead to pollution of the drinking water supply include:
- Firefighters plugging into city hydrants;
- Computer industries using plating practices;
- Farmers or florists using irrigation systems; and
- Landowners mixing water from wells, ponds, streams or other sources with city water.
Tips to Protect Your Home Water Supply
Cross connections often happen at home. Everyday activities - such as filling your pool or spa, washing your car, or fertilizing your garden with a hose-end sprayer - can lead to backlfow.
Here are ways that you can prevent backflow at home:
- Check appliances that use water (dishwashers, etc.) for proper drainage.
- Check that your toilet tanks are working correctly.
- Never place a hose connected to your water supply directly into the water in a sink, drain, swimming pool, koi pond, or chemical sprayer. To fill your pool or spa, set the hose above the rim.
- If you are using a sprayer powered by a hose, use a vacuum breaker to prevent chemicals from siphoning back into your water supply.
- If you have a pool or spa with a permanently installed fill line, make sure a backflow preventer is properly installed in the line connected to your drinking water. Irrigation systems need protection too.
County Services
The Cross Connection Control Program protects the public drinking water supply in San Mateo County.
Inspectors check industries, irrigation systems and other water distribution systems to find cross connections and prevent backflow.
Tester certified by the County conduct tests on backflow prevention devices on a regular basis.
Besides conducting inspections and certifying testers, Cross Connection Control staff work with large water suppliers in the following ways:
- ensure that the potable water supply is protected by the installation of backflow preventers and the annual maintenance/testing of these devices;
- checking plans;
- consulting about how to prevent backflow;
- providing a list of approved prevention devices and guidelines for installing them; and
- training personnel.
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