Drinking Water Regulations
Primary Drinking Water
Regulation: A
regulation defined in the federal Safe Drinking Water Act that
specifies contaminants that may have an adverse effect on the
health of persons. It
specifies a maximum contaminant level (MCL) for each contaminant
and contains criteria and procedures for compliance. The District criteria meet
or exceed these criteria for lead, copper and total
colifom.
Note: Schools are not
required to meet the federal primary drinking water requirements,
but the School Board will consider adopting its own
standards.
Secondary Drinking Water
Regulation: A US
EPA non-enforceable regulation for a contaminant that may adversely
affect the taste, odor, or appearance of water, but not adversely
affect health.
Secondary maximum contaminant levels (SMCLs) have been established
for secondary contaminants.
Description of Contaminants /
Constituents Being Sampled
Turbidity is a measurement of the relative
cloudiness of the water caused by the presence of suspended matter
or air bubbles, resulting in the scattering and absorption of
light. Turbidity is a
general indicator of water quality, both from a health and an
aesthetic standpoint.
The units of measurement for turbidity are "nephelometric turbidity
units" (NTU). Low
turbidity values indicate very clear water with relatively few
particles, while higher turbidity values indicate greater numbers
of particles and degraded water quality. At turbidity values less
than about 5 NTU, there is no cloudiness perceptible to the human
eye - the water looks perfectly clear. For water samples taken
from older steel plumbing (as is most common in Seattle schools),
the source of turbidity is almost completely attributable to iron
oxide (rust) particles that are not harmful to human
health.
Color is a physical characteristic describing
the appearance of water (different from turbidity, which is the
cloudiness of water).
Color is measured in "color units" (CU), with larger numbers
indicating stronger color. Generally, color measured
at 5 CU or less has no apparent color to the naked eye. For water samples taken
from older steel plumbing (as is most common in Seattle schools),
the source of color is almost completely attributable to iron oxide
(rust) particles which are not harmful to human health.
Coliform Bacteria are
organisms that are present in the environment and in the feces of
all warm-blooded animals and humans. Coliform bacteria will
likely not cause illness. However, the presence of coliform
bacteria in drinking water indicates that disease-causing organisms
(pathogens) may be present in the water system, so testing for
coliform bacteria is a long-standing method for assessing drinking
water quality that is accepted by all public health
agencies.
There are three forms of
coliform bacteria that are commonly tested for in drinking water:
total coliform, fecal coliform, and E.coli. The total coliform group
encompasses a large collection of different types of bacteria that
are very commonly found in the environment (e.g., soil and
vegetation), and are generally harmless. Fecal coliform bacteria
are a sub-group of the total coliform group. They appear in great
quantities in the intestines and feces of humans and animals. If only total coliform
bacteria are detected, the source is probably environmental. However, if environmental
contamination can enter a water system, there may be a pathway for
pathogens to enter as well, so it is important to identify the
source if possible and correct the problem. The presence of fecal
coliform in a drinking water sample often indicates recent fecal
contamination and a greater risk of exposure to pathogens. E. coli is a sub-group
of the fecal coliform group. Most E. coli are harmless and
are also found in the intestines and feces of humans and
animals. However, some
strains may cause illness, so the presence of E. coli in a drinking water
sample almost always indicates recent fecal contamination and a
greater risk of pathogens being present. [A note about E. coli: Most E. coli outbreaks have been
related to food contamination and are caused by a specific strain
of E. coli known as E. coli O157:H7]. When a water sample is
reported as "E. coli
present", it does not mean that this specific strain is present and
in fact it is most likely not present. However, it does indicate
fecal contamination and the appropriate protective measures will be
made.
Drinking water samples
collected at various locations in the schools are tested for total
coliform. If total
coliform is present, the sample is then also tested for E. coli.
More information on coliform
bacteria is available at the Washington State Department of
Health's web site for drinking water: http://www.doh.wa.gov/ehp/dw.
Chlorine Residual is the concentration of chlorine
compounds that serve as disinfectants in the drinking water
supply. Chlorine is
added to all water supplied in the City of
Seattle.
Lead is a metallic element that is commonly
found in red brass alloys used in faucet and drinking fountain
fixtures of all types, as well as in lead-tin solder that was
commonly used for joining copper plumbing pipes until 1992. Lead enters tap water via
chemical and physical interactions between the water and the
materials. Lead is not
normally found in source water supplies; Seattle's water supply has virtually no
lead. It is a
regulated contaminant for health concerns.
Cadmium is a metallic element that is
present in trace amounts in zinc (galvanized) coatings. Cadmium enters tap water
via chemical and physical interactions between the water and the
pipe materials.
Cadmium is not normally found in source water supplies; Seattle's
water supply has virtually no cadmium. It is a regulated
contaminant for health concerns.
Copper enters tap water via chemical and
physical interactions between the water and copper piping and brass
alloys found in fixtures. Copper is generally a
concern for aesthetic reasons because it can cause staining of
fixtures and hair, but it is also a health concern at higher
concentrations for persons with a relatively rare disease called
Wilson's Disease.
Zinc enters tap water via chemical and
physical interactions between the water and galvanized steel
pipes. Zinc is not a
regulated contaminant for health reasons, but is regulated to limit
its concentrations in wastewater.
Iron is present in very low levels in
Seattle's water supply, but is present in tap water primarily
because of chemical and physical interactions between the water and
older steel and iron pipes in buildings. Iron is not a regulated
contaminant for health reasons, but is regulated because of
aesthetic problems like staining of fixtures and discolored
water.
