Polluted water or sewage may carry such diseases as typhoid fever and
amoebic dysentery. If you do your own plumbing work, be sure that--
There are no leaks in drainpipes through which sewage or sewage gases
can escape.
There are no cross connections between piping carrying water from
different sources unless there can be reasonable certainty that all
sources are safe and will remain safe.
There can be no back siphonage of water from plumbing fixtures or
other containers into the water-supply system.
Once a pipe has become polluted, it may be difficult to free it of
the pollution. For this reason, building codes do not permit the use
of second-hand pipe. All initial piping and parts and subsequent
replacements should be new.
Since a plumbing system will require service from time to time,
shutoff valves should be installed at strategic locations so that
an affected portion can be isolated (water flow to it cut off) with
minimum disturbance to service in the rest of the system. Shutoff
valves are usually provided on the water closet supply line, on the
hot- and cold-water supply line to each sink, tub, and lavatory, and on
the water heater supply line. Drain valves are usually installed for
water-supply piping systems and for hot-water storage tanks.
A pressure-relief valve should be installed for the water heater
storage tank to relieve pressure buildup in case of overheating.
[Illustration: _Figure 3._--Frostproof hydrant; _A_, Closed; _B_,
opened. As soon as the hydrant is closed, water left in the riser
drains out the drain tube as shown in _A_. This prevents water from
freezing in the hydrant in cold weather.]