Post by PeterDBuzz... Wrong answer. Since there is no such thing as 'intact' (after
all there is a faucet, and whatever else that is attached) this
concept doesn't apply.
Well, your arguements are pretty much nonsense. Faucets, urinals, water
closets, sinks, drinking fountains, washing machines, ice makers, etc. all
have backflow prevention built-in in the form of an air gap. Backflow
prevention is present at all openings into the system (where ever a source
of polution can occur).
The real danger in back-siphoning is the common garden hose lying in a pool
polluted water. Many older homes do not have back-flow protection on their
hose bibs, and should a condition of low or loss of pressure such as drawing
water from a hydrant by a fire engine, can drop water pressure low enough to
siphon water from down stream (this has actually happened near major fires
when several pumpers were connected.) Anyway, so long as a system is air
tight, water does not go stagnant (remember that municipal supplies use
ozone or chlorine to maintain sterilization until comming into contact with
the outside air.)
Note that the code does not require the use of backflow prevention in the
average home supply. It's common practice to allow water heated in a
domestic water heater to expand back into the public supply (city mains).
If a *local ordinance* requires a backflow prevention device, due to a
private supply, or the supply serves a boiler, or if the residence lies in
an area subject to flooding, or for fire suppression equipment (double check
vales would be required here), or for any other reason, then it's required
to install an expansion tank after the check valve.
Installing a check valve in a supply main can be dangerous; when a tank-type
water heater is installed. If water cannot expland (due to a check valve in
the supply) dangerous high pressure can develop (under certain conditions)
whch can damage the piping or water heater. It's for this reason that a
expansion tank is required whenever a check valve is installed). (Private
supplies alreay have an expansion tank as a necessary part of the well/pump
operation).
Check valves in the main supply are not a requirement of the model codes (at
least that I'm aware of; IRC and UPC). If you know of a reference to any
requirement mandating the installation of a backflow prevention device (in
the form of a check valve) in a supply from a municipal main, please post it
here as I would certainly be interested in reading it.
Post by PeterDWhat happens is related to a number of pre-existing problems that
occured some years ago. The biggest one was where some pesticide and
fertilizer companies, and companies making things like car washers
I agree that ground water contamination is always a problem. In my area we
have had water supply pollution due to leaking underground gasoline storage
tanks. In another example, a nearby village was forced to shut down
supplying water for several days due to farm pesticide runoff contaminating
the ground water in a local pumping station. (He had an open, abandoned
well that extended down to the depth of the municipal level.)