Pressure Vacuum Breaker
What is a backflow?
An undesirable reversal of flow of a liquid, gas or solid into the potable water supply. A backflow preventer keeps this from happening. Allow me to give you a word illustration.
If you have drank a beverage through a straw you have created a vacuum by suction, the same thing happens when higher pressure fluids, gases, or suspended solids move to an area of lower pressure fluids. This is back-siphonage and an example of an indirect cross-connection.
Now imagine using that same beverage with straw and now you blow air through the straw and bubbles begin to erupt at the submerged end, you have now created back-pressure. If your breath had been, let us say natural gas, you would have forced that gas into a potable water tank and it in turn could be carried to your kitchen faucet. This is an example of a direct cross-connection.
Just one of many reported incidents!
Not picking on anyone, just let's get it fixed
In your home exists many possibilities for backflow to occur, We should always be aware of what we are putting the end of our hoses to, If you have an anti-siphon hose bib, it will have a circular disc shaped piece on top, someone was doing some forward thinking. But they don't last forever as they are susceptible to freeze damage and general wear and tear.
Another potential for cross-connection (backflow) to occur is on that same anti-siphon hose bib when you hook up a power washer to it, remember the key compound word here is (anti-siphon) the pressure in the pump on the power-washer can overcome the pressure coming from your hose-bib and then it can introduce cleaning chemicals into your homes water system. It would be smarter to have the contractor or you, fill an external tank to draw your water supply from, problem solved.
Just in this one example you can see how a common task could be having an adverse effect on your families well-being. These anti-siphon hose bibs only offer protection against back-siphonage and not back-pressure. If you have no device currently in place on your hose connections, my advice to you is to buy and install now.
Another place in the home for back-pressure and back-siphonage to occur with potentially harmful contaminants? The BOILER! Yup that old boiler is full of old water quality deprived, mineral and chemical infused liquid that looks like triple boiled coffee and you din't want any. For this type of water feed connection you will at a minimum need a dual check, and truly these should be replaced every five (5) years as they are not testable.
Reduced Pressure Zone Assembly
My handywork, protecting H2O, Fire Training
Low degree hazard backflow w/vent
Dual check made by Watts (7D)
EPA Cross-Connection Control Manual
A very informative manual about backflow prevention.
Testing and repair of backflow preventers
The backflow preventer has moving parts, and therefore just as automobiles and houses need repair, the same goes for these pollution prevention control apparatus. Once every 365 days these assemblies that are testable, need to have done just what the description implies, they need to be tested. The purpose of this test is to interpret from the results of the test whether or not the backflow is working properly.
If they are found out to have failed, they will need to be cleaned and/or repaired and re-tested until they pass the test. Many plumbing companies are able to provide this service, and depending on your state or countries plumbing codes, perhaps fire sprinkler and/or landscape irrigation contractors might also do the same.