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Why is a backflow preventer required on lawn sprinkler systems?
Monday, July 9, 2018
Homes that use the same water source for their potable/drinking water and for a landscape sprinkler system have the potential for a backflow of contaminated water when there is a loss of pressure in the system. It doesn’t matter whether it is municipal water or a well. The vacuum created by the pressure loss can suck water backwards into the drinking water system, which is a health hazard.
The backflow in a sprinkler system is one type of “cross connection,” which is defined as a point in a faulty plumbing system where polluted water can flow into the potable water piping and contaminate it. A little dirt or bacteria backing up into your drinking water may seem innocuous, but there are documented cases of illness and even death from the backflow of contaminated water. It was the bane of ancient plumbing systems dating back to the Roman Empire, when a flawed pipe configuration would allow sewage to seep into the fresh water supply.
So the International Building Code (IRC) has the following requirement:
P2902.5.3 Lawn irrigation systems. The potable water supply to lawn irrigation systems shall be protected against backflow by an atmospheric-type vacuum breaker, a pressure-type vacuum breaker or a reduced pressure principle backflow preventer. A valve shall not be installed downstream from an atmospheric vacuum breaker. Where chemicals are introduced into the system, the potable water supply shall be protected against backflow by a reduced pressure principle backflow preventer.
The most common backflow prevention device is an pressure-type vacuum breaker, as shown below. Insulation for the above-ground piping is recommended for colder climates, where pipe fractures might be caused by a hard winter freeze. Also, some jurisdictions require an annual inspection of residential backflow preventers to confirm that they are still functional.
Sprinklers that are professionally installed by a licensed contractor always have a backflow preventer, but a homeowner-installed sprinkler system with no vacuum breaker is a fairly common defect we find during our home inspections.
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