Public
health officials have always been concerned about cross connections
and backflow in plumbing systems and in public drinking water supply
distribution systems. People have utmost confidence in the water
they drink. Open a faucet and we drink what comes out. If, however,
the water is contaminated, sickness and even death can be the
result. Community awareness can greatly reduce the chance for cross
connections and backflow incidences.
Cross-Connection and Backflow Defined
A cross-connection is a direct or indirect connection between
a potable water system and any other liquid, gas, or other
substance. A direct connection is a physical link between the piping
arrangements of a potable and non-potable system. An indirect
connection is where the water itself makes the connection such as a
hose from a potable supply submerged in contaminated water, or a
leaking pipe that "pools" water around the break.
Backflow is the unwanted reverse flow of water, gases or
other substances into a potable water supply distribution system. It
can potentially occur at any time there is a cross connection
between the potable supply and any source of pollution or
contamination.
Sources of contamination and how
you can be affected.
Examples of likely contamination sources are wash basins,
sinks, dishwashers, garbage disposals, showers, bathtubs, toilets,
and hose bibbs (faucet to which a hose may be attached or buried
yard hydrants).
Cross connections and unwanted backflow have serious health
implications. Many cases have been documented tracing serious
disease outbreaks directly to a specific cross-connection and
backflow condition in a potable system. These cases have been
particularly prevalent for underground sprinkler systems, submerged
hoses, and at or near commercial facilities with high-hazard
non-potable uses such as hospitals and industrial sites. Although
major disease outbreaks get plenty of publicity, it is likely many
backflow events occur in small systems and go unnoticed. This is
because too few people may be affected to create a public stir, or
persons who become ill may just think they have the flu.
What you can do to
prevent cross-connections in your home.
Point-of-use backflow preventers are the best way to protect
the water you drink everyday. There are many types of approved
backflow preventers. The three most used by the general public
include the: Air gap, Atmospheric vacuum breaker (AVB), and the
Pressure vacuum breaker assembly (PVB), Each backflow
preventer type described in this section is designated as a
method, a device, or an assembly.
Specific criteria apply to each.
An air gap is a method for backflow prevention that is
considered the ultimate backflow preventer, although it is
relatively easy to circumvent in unmonitored situations. An air gap
should be used whenever
appropriate, before any other type of preventer is considered. An
air gap is defined as the physical separation between a potable and
non-potable system by an air space. The best example of this is the
standard design of all types of sinks where there is a separation
between the free-flowing discharge of the
faucet and the overflow rim of the receiving basin. (pictured at
right)
An
atmospheric vacuum breaker (AVB) is a device
consisting of a body, a checking seat, and an atmospheric vent.
During normal operation, potable water seals off the vent. If a
negative pressure develops in the supply line the check valve drops
to seal the opening while the vent opens to admit air to break the
vacuum.
A hose bibb vacuum breaker (HBVB) is a type of AVB (pictured at
left). The HBVB is a
device with a metal body, a springloaded check valve, and air
inlets. It is one of the simplest and cheapest ways of preventing
low and high hazard back-siphonage through hoses attached to
threaded connections. These can and should be installed on all
threaded connections, sill cocks, and yard hydrants where there is
any possibility a hose will be attached for any purpose. HBVBs are
available with a means to manually drain the device for freezing
conditions. Click here to see the HU approved HBVB.
A pressure vacuum breaker assembly (PVB) is an assembly
consisting of a loaded air inlet valve, an internally loaded check
valve, two properly located test cocks, and two isolation valves.
PVBs are suitable for low and high hazard back-siphonage
installations, the same as AVBs. Unlike AVBs, PVBs may have valves
downstream and be under continuous pressure. Typical installations
include swimming pools, heat exchangers, degreasers and livestock
water systems. They are most often used in sprinkler irrigation
systems with downstream control valves (pictured at right).
For more information on how to prevent
cross-connections contact the Hastings Utilities Water Department by
calling (402)463-1371 or
email us.
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