DRINKING
WATER QUALITY STANDARDS & GUIDELANDS
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EPA
National Primary Drinking Water Standards (EPA, 2002)
| Microorganism |
MCLG1
(mg/L) |
MCL
or TT
(mg/L) |
Potential
Health Effects from Ingestion via Water |
Sources
of Contaminant in Drinking Water |
| Cryptosporidium2 |
as
of 01/01/02: zero |
as
of 01/01/02: TT |
Gastrointestinal illness (e.g., diarrhea, vomiting, cramps) |
Human and animal fecal waste |
| Giardia lamblia2 |
zero |
TT |
Gastrointestinal illness (e.g., diarrhea, vomiting, cramps) |
Human and animal fecal waste |
| Heterotrophic plate count (HPC)2 |
n/a |
TT |
HPC has no health effects, but can indicate how effective treatment
is at controlling microorganisms. |
HPC measures a range of bacteria that are naturally present
in the environment |
| Legionella2 |
zero |
TT |
Legionnaire's Disease, commonly known as pneumonia |
Found naturally in water; multiplies in heating systems |
| Total Coliforms (including fecal coliform and E. Coli)2 |
zero |
5.0%3 |
Used as an indicator that other potentially harmful bacteria
may be present4 |
Coliforms are naturally present in the environment; fecal coliforms
and E. coli come from human and animal fecal waste. |
| Turbidity |
n/a |
TT |
Turbidity is a measure of the cloudiness of water. It is used
to indicate water quality and filtration effectiveness (e.g.,
whether disease-causing organisms are present). Higher turbidity
levels are often associated with higher levels of disease-causing
microorganisms such as viruses, parasites and some bacteria.
These organisms can cause symptoms such as nausea, cramps, diarrhea,
and associated headaches. |
Soil runoff |
| Viruses (enteric) |
zero |
TT |
Gastrointestinal illness (e.g., diarrhea, vomiting, cramps) |
Human and animal fecal waste |
|
Notes:
- Definitions:
- Maximum
Contaminant Level (MCL): The highest level of a contaminant
that is allowed in drinking water. MCLs are set as close to
MCLGs as feasible using the best available treatment technology
and taking cost into consideration. MCLs are enforceable standards.
- Maximum
Contaminant Level Goal (MCLG): The level of a contaminant
in drinking water below which there is no known or expected
risk to health. MCLGs allow for a margin of safety and are
non-enforceable public health goals.
- EPA's surface water treatment rules require systems using surface
water or ground water under the direct influence of surface
water to (1) disinfect their water, and (2) filter their water
or meet criteria for avoiding filtration so that the following
contaminants are controlled at the following levels:
- Cryptosporidium:
(as of January 1, 2002) 99% removal/inactivation
- Giardia
lamblia: 99.9% removal/inactivation
- Viruses:
99.99% removal/inactivation
- Legionella:
No limit, but EPA believes that if Giardia and viruses are
removed/inactivated, Legionella will also be controlled.
- HPC:
No more than 500 bacterial colonies per milliliter.
- Turbidity:
At no time can turbidity (cloudiness of water) go above 5
nephelometric turbidity units (NTU); systems that filter must
ensure that the turbidity go no higher than 1 NTU (0.5 NTU
for conventional or direct filtration) in at least 95% of
the daily samples in any month. As of January 1, 2002, turbidity
may never exceed 1 NTU, and must not exceed 0.3 NTU in 95%
of daily samples in any month
- No more than 5.0% samples total coliform-positive in a month.
(For water systems that collect fewer than 40 routine samples
per month, no more than one sample can be total coliform-positive).
Every sample that has total coliforms must be analyzed for fecal
coliforms. There may not be any fecal coliforms or E. coli.
- Fecal
coliform and E. coli are bacteria whose presence indicates that
the water may be contaminated with human or animal wastes. Disease-causing
microbes (pathogens) in these wastes can cause diarrhea, cramps,
nausea, headaches, or other symptoms. These pathogens may pose
a special health risk for infants, young children, and people
with severely compromised immune systems.
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WHO
bacteriological quality of drinking water (WHO, 19961)
Microorganisms |
Guideline
values |
All water intended for drinking
|
E.coli or thermotolerant coliform bacteria2,3 |
Must
not be detectable in any 100ml sample |
Total
coliform bacteria |
Must
not be detectable in any 100ml sample |
Treated water entering the distribution system
|
E.coli or thermotolerant coliform bacteria2 |
Must
not be detectable in any 100ml sample |
Total
coliform bacteria |
Must
not be detectable in any 100ml sample |
Treated water in the distribution system
|
E.coli or thermotolerant coliform bacteria2 |
Must
not be detectable in any 100ml sample |
Total
coliform bacteria |
Must
not be of samples detectable in any 100ml sample. In the case
of large supplies, where sufficient samples are examined,
must not be present in 95% of samples taken throughout any
12-month period |
|
Notes:
- Immediate
investigative action must be taken if either E.coli or total
coliform bacteria are detected. The minimum action in the case
of total coliform bacteria is repeat sampling; If these bacteria
are detected in the repeat sample, the cause must be determined
by immediate further investigation.
- Although
E.coli is the more precise indicator of fecal pollution, the
count of thermotolerant coliform bacteria is an acceptable alternative.
If necessary, proper confirmatory tests must be carried out.
Total coliform bacteria are not acceptable indicators of the
sanitary quality of rural water supplies, particularly in tropical
areas where many bacteria of no sanitary significance occur
in almost all untreated supplies.
- It
is recognized that, in the great majority of rural water supplies
in developing countries, fecal contamination is widespread.
Under these conditions, the national surveillance agency should
set medium-term targets for the progressive improvement of water
supplies, as recommended in Volume 3 Guidelines for drinking-water
quality.
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