Building Design and Construction Handbook - Merritt - Ventech!

WATER-SUPPLY, SPRINKLER, AND WASTEWATER SYSTEMS 14.5
Organic Content. Bacteriological tests of water must be made on carefully taken
and transported samples. A standard sample is five portions of 10 cm 3 , each sample
a different dilution of the water tested. A state-certified laboratory will use approved
standard methods for analyses.
Organisms other than bacteria, such as plankton (free-floating) and algae, can
in extreme cases be important factors in design of water treatment systems; therefore,
biological analyses are significant. Microscopic life and animal and vegetable
matter can be readily identified under a high-powered microscope.
Maintenance of Quality. It is not sufficient that potable water just be delivered
to a building. The quality of the water must be maintained while the water is being
conveyed within the building to the point of use. Hence, the potable-water distribution
system must be properly designed to prevent contamination.
No cross connections may be made between this system and any portion of the
wastewater-removal system. Furthermore, the potable-water distribution system
should be completely isolated from parts of plumbing fixtures or other devices that
might contaminate the water. Backflow preventers or air gaps may be used to prevent
backflow or back siphonage. Many states or municipal water systems now
have regulations which require that backflow prevention devices be installed at the
building potable and fire system services. These devices are required to protect the
municipal water systems from contamination. All backflow prevention devices are
required to have annual inspection, testings and certification.
Backflow is the flow of liquid into the distribution piping system from any
source other than the intended water-supply source, such as a public water main.
Back siphonage is the suction of liquid back into the distribution piping system
because of a siphonage action being applied to the distribution pipe system. The
type of backflow preventer to use depends on the type of reverse flow expected
(backflow or back siphonage) and the severity of the hazard. In general, double
check-valve-type backflow preventers are normally approved for low-hazard backflow
conditions and vacuum breakers are approved for low-hazard back-siphonage
conditions. Where the hazard is great, reduced-pressure principal backflow preventers
are normally required. The local code authorities should be consulted about
local and state regulations pertaining to backflow prevention.
14.4 WATER TREATMENT
To maintain water quality within acceptable limits (Art. 14.3), water supplied to a
building usually must undergo some form of treatment. Whether treatment should
be at the source or after transmission to the point of consumption is usually a
question of economics, involving hydraulic features, pumping energies and costs,
and possible effects of raw water on transmission mains.
Treatment, in addition to disinfection, should be provided for all water used for
domestic purposes that does not fall within prescribed limits. Treatment methods
include screening, plain settling, coagulation and sedimentation, filtration, disinfection,
softening, and aeration. When treatment of the water supply for a building is
necessary, the method that will take the objectionable elements out of the raw water
in the simplest, least expensive manner should be selected.
Softening of water is a process that must be justified by its need, depending on
use of the water. With a hardness in excess of about 150 ppm, the cost of softening
will be offset partly by the reduction of soap required for cleaning. When synthetic