University of Idaho logoQuality Water
for Idaho
Current
Information
Series No. 874
Drinking Water Standards
Roy Taylor, Ernestine Porter and Robert L. Mahler

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Health Concerns
Contaminants in drinking water always are cause for concern. However, it is important to distinguish between the acute and chronic effects of harmful substances.

Acute Effects

Acute effects appear shortly after ingestion of contaminated water, usually within several weeks. They ususally appear soon after exposure to a toxic substance. For example, a farmer who accidentally spills a pesticide may shortly thereafter suffer nausea, dizziness and vomiting.

In Idaho and the rest of the nation the most commonly detected drinking water problem is bacterial contamination caused by improper well construction and maintenance. Bacterial contamination is a common cause of acute toxicity, producing symptoms as mild as upset stomach and diseases as serious as dysentery, typhoid fever and hepatitis. Household cleaners and garden chemicals are other examples of contaminants that can produce acute effects.

Chronic Effects

Chronic effects appear after longer incubation periods, possibly even after a number of years. Chronic effects result from exposure to a substance over weeks or years. For example, a coal miner who breathes traces of coal dust for many years may later develop serious respiratory problems.

Over time, some drinking water contaminants can damage the liver, kidneys, heart and other body organs. Health officials are almost always concerned about chronic effects of drinking-water contaminants such as low-level nitrates, radon and volatile organic chemicals. Such effects may include cancer or damage to the central nervous system.

Drinking Water Standards
The Environmental Protection Agency (EPA) standards for drinking water fall into two categories -- primary standards and secondary standards.

Primary Standards

Primary standards are based on health considerations and are enforced by the EPA. They protect you from three classes of toxic pollutants: pathogens, radioactive elements and toxic chemicals. Primary standards set a limit, called the maximum contamination level (MCL), on the highest allowable concentration of a contaminant in drinking water supplied by municipal water systems. The MCL is usually espressed in milligrams per liter (mg/l), which is the same as parts per million (ppm).

Secondary Standards

Secondary standards cover contaminants that cause offensive taste, odor, color, corrosivity, foaming and staining. The concentration limit is called the secondary maximum contaminant level (SMCL). Secondary standards are not enforced. They are guidelines for water treatment plant operators and state governments attempting to provide communities with the best possible water quality.

Idaho Standards

The state of Idaho has established water quality standards based on the actual or intended use of water. These uses include domestic, agricultural and recreational uses and use for aquatic organisms.

Contaminants or potential contaminants covered by Idaho regulations include hazardous, deleterious and radioactive materials; floating, suspended or submerged matter; excess nutrients; oxygen-demanding materials and sediment. Standards for Idaho water quality are established and enforced by the Division of Environmental Quality, Idaho Department of Health and Welfare. While existing standards help ensure safe water, standards do not exist for many additional contaminants.

Idaho standards for domestic water supplies.
SubstanceMaximum allowable concentration
(mg/l or ppm)
Arsenic0.050
Barium1.000
Cadmium0.010
Chromium0.050
Cyanide0.200
Flouride*
Degrees
up to 12.0 C (54 F)2.400
12 C (55 F) -- 15 C (58 F)2.200
15 C (59 F) -- 18 C (64 F)2.000
18 C (65 F) -- 21 C (71 F)1.800
22 C (72 F) -- 26 C (79 F)1.600
26 C (80 F) -- 32 C (90 F)1.400
Lead0.050
Mercury0.002
Nitrate (as N)10.000
Selenium0.010
Silver0.050
Endrin0.0002
Lindane0.004
Methoxychlor0.100
SodiumNo maximum established;
20 suggested as optimum
Toxaphene0.005
Trihalomethanes0.100
2, 4-D0.100
2, 4, 5-TP Silvex0.010
Coliform bacteria2 per hundred milliliter (ml)
for any individual sample
Turbidity5 nephelometric turbidity units
(NTU) for any individual sample
* As determined by the average annual maximum daily air temperature for the area where the water is to be used.

The Authors -- Roy Taylor is Extension agricultural engineer, Ernestine Porter is Extension textiles and clothing specialist and Robert L. Mahler is soil scientist and Extension water quality coordinator, all in the University of Idaho College of Agriculture, Moscow.

Idaho This publication is one of a series on water quality issues produced by the University of Idaho Cooperative Extension System for the people of Idaho. The material is based upon work supported by the U.S. Department of Agriculture, Extension Service, under special project number 90-EWQUI-1-9216.

UI College of Agricultural and Life Sciences

Issued in furtherance of cooperative extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, LeRoy D. Luft, Director of Cooperative Extension System, University of Idaho, Moscow, Idaho 83844. The University of Idaho provides equal opportunity in education and employment on the basis of race, color, religion, national origin, gender, age, disability, or status as a Vietnam-era veteran, as required by state and federal laws.
8M 9-90, 400 2-93 (reprint)
Printed with special grant funds from USDA

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Revised: January 3, 2002
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