What is a Cross Connection?

BP AssemblyYou bought a house that has an irrigation well on the property that is connected to the landscape irrigation system, but you also have a city water connection for your drinking water. You are very happy because you are going to save money on your water bill! In case the well pump stops working, your landscape irrigation system is also connected to your home’s water supply system. When there are connections between a drinking (potable) water system and any other water source or system, this is called a cross-connection.

One day, your neighbor fills a glass of water from the tap and notices the water is cloudy and has a metallic taste. What could this be from? Well, it is possible that a decrease in the public water system pressure caused water from your well to be pumped back into the public drinking water system. This is called backflow, or the undesirable reversal of flow of water or other substances back into the drinking water supply. When this occurs, the water pressure may be greater from your alternate water source than the pressure from the public water supply. If there are any cross-connections, pollutants and contaminants may be introduced into the drinking water supply lines, and then carried into the public water system, and therefore to other customers on the public water system. In 2011, a backflow event took place in Redwood City, affecting several hundred customers under just such an irrigation well scenario.

Environmental Health takes cross-connections and backflows very seriously, as potential for contamination of the water supply could affect thousands of people. Through the Cross-Connection Control Program, Environmental Health and/or your water agency inspects all properties that have alternative sources of water to assure installation of a plumbing fixture called a Backflow Prevention Assembly (BPA). BPA’s prevent non-potable water (such as landscape irrigation, fire sprinkler systems, boiler systems or alternate water supplies like water wells and tanks) from flowing back into the drinking water supply. BPAs may be required to be installed at the water service meter(s) and/or inside a building to isolate equipment that may subject the water system to contamination. Your water company is required by the State Drinking Water Division (State Water Resources Control Board) to prevent backflow incidents to the public drinking water supply. To ensure cross-connections to the public drinking water system are minimized, your water agency is responsible for ensuring an effective Cross-Connection Control Program. Many water agencies in San Mateo County contract with Environmental Health to make sure they are in compliance with the law.

BPAs need to be tested upon installation and annually thereafter by a County-certified Backflow Prevention Assembly Tester. San Mateo County mails out test-notice reminders to BPA owners throughout the year. If the assembly passes the annual field test, the tester will hang a numbered backflow tag from the assembly and submit the test results to San Mateo County. Failure to test BPAs annually may result in enforcement actions by San Mateo County and the Water Purveyor.

For more information about the San Mateo County Cross-Connection Control Program, please call (650) 372-6200 or visit http://smchealth.org/crossconnection.

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