A gardener just installed a drip irrigation system in my backyard. He didn't installed the back-flow preventer. When I asked him why, he told me for drip irrigation you don't need the back-flow preventer! His argument was that in drip irrigation, we have to install a pressure reducer so there is no need for a back-flow preventer.
Is he right on his argument?
I think he is mistaken. A pressure reducing valve is not listed in the code among the approved backflow prevention devices:
2009 Uniform Plumbing Code 603.4.6 Protection From Lawn Sprinklers and Irrigation Systems
603.4.6.1 Potable water supplies to systems having no pumps or connections for pumping equipment, and no chemical injection or provisions for chemical injection, shall be protected from backflow by one of the following devices:
(1) Atmospheric vacuum breaker (2) Pressure vacuum breaker (3) Spill-resistant pressure vacuum breaker (4) Reduced pressure vacuum breaker
Please note that this is for your own safety. It keeps you from drinking water that's been contaminated by nasty things such as animal feces, dead critters, fertilizers, or even pesticides. It keeps you from being sued by your neighbors if they get sick. As it is a law in Texas, even rural areas, we have to abide by it. $100.00 for a PVB with fittings is cheap for the piece of mind.
See:
ยง344.50. Backflow Prevention Methods.
(a) Any irrigation system that is connected to a public or private potable water supply must be connected through a commission-approved backflow prevention method. The backflow prevention device must be approved by the American Society of Sanitary Engineers; or the Foundation for Cross-Connection Control and Hydraulic Research, University of Southern California; or the Uniform Plumbing Code;
It is also important to install back-flow preventers to discourage clogging of the drippers. After the irrigation cycle finishes, the volume of the pipe that was full of water will need to be replaced by air or it will collapse at certain points. If there is no 'vacuum breaker' type valve the air will enter the line through the dripper aperture bringing with it dirt and debris. If you want to decrease clogging of drippers and occurrence of dry-spots in the garden, I'd recommend installing such a device at the highest point of each station. If the line is very long, put one every 30 metres or so.
Even if it isn't code were you reside it would be wise to install one for your health. But check the valves that you have installed. Many irrigation valve manufacturer's make back flow valves built into them. It's usually just above the out flow threads on the valve. Or if you shake the valve you should hear it rattle. that is the check valve that allows water to only flow in one direction.
