Environmental Protection Agency Safe Drinking
Water Act Standards:
Microbiological, Radiological, and Inorganic Contaminants
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Drinking Water Standards for Contaminants: Microbiological, Radiological, and Inorganic Contaminants (PDF)
This is a list of the radiological and inorganic contaminants that are tested for in public water systems (those that provide water to the public), along with an explanation of the testing done for microbiological contaminants.
For microbiological contaminants, nitrate, and nitrite, the potential health effects can be immediate; for the others, the contaminant would have to be consumed at elevated levels over a long period of time for there to be any chance of adverse health effects.
The federal standard for most contaminants is listed as a Maximum Contaminant Level (MCL), the lowest concentration at which that particular contaminant is believed to represent a potential health concern. Unless otherwise noted, the MCL is expressed as parts per billion (ppb). Because of technological limitations or other factors, it is not possible to test for some contaminants in a reliable fashion. Instead, public water systems are required to use specific Treatment Techniques (TT) that are designed to remove these particular contaminants from the water.
In addition to the contaminants listed, monitoring is done for additional inorganic chemicals for which MCLs have not been established. If unacceptable levels are found of these unregulated contaminantsbased on established state health standards and an assessment of the risks they posethe response is the same as if an MCL has been exceeded: the public water system must notify those served by the system.
(Note: This fact sheet covers only microbiological, radiological, and inorganic contaminants. For a list of other contaminants that are monitored, refer to the Minnesota Department of Health fact sheet, Drinking Water Standards for Contaminants: Volatile and Synthetic Organic Chemicals.
MCLMaximum Contaminant Level
ppbparts per billion
ppmparts per million
Microbiological organismsincluding bacteria, protozoa, and virusesare among the oldest health threats to drinking water quality and the agents currently responsible for most waterborne diseases. Unfortunately, specific disease-producing organisms present in water are not easily identified. For this reason, an indicator organism, one that indicates that pathogenic organisms may be present, is used. A group of closely related bacteria, the total coliform group, has been selected as an indicator of harmful organisms in drinking water.
The Maximum Contaminant Level for microbiological contaminants is based on the presence or absence of total coliforms in a sample, rather than on coliform density. The Maximum Contaminant Level for coliforms depends on the number of samples collected per month. If fewer than 40 samples are collected each month, no more than one may contain coliform bacteria. If 40 or more samples are collected each month, no more than five percent may contain coliform bacteria.
Also termed radionuclides, radiological contaminants can enter water from some soils, from the disposal and storage of radioactive wastes, or from the mining of phosphorus or uranium. While these elements are usually naturally occurring, contamination of drinking water from radionuclides may be from human-made sources.
Combined radium-226 and radium-228*
5 picocuries per liter
Gross alpha particle activity (including radium-226 but excluding radon and uranium)
15 picocuries per liter
Inorganic chemicals are metals, salts, and other compounds that do not contain carbon. These chemicals sometimes contaminate water supplies as a result of human activity; however, many are naturally occurring in certain geographic areas. In addition, fluoride is added to water supplies in small amounts to enhance dental care, although if the water contains too much fluoride, it can result in adverse effects, such as mottling of the teeth.
|Inorganic Contaminants||MCL (ppb)*||Potential Health Effects|
|Arsenic||10||Dermal, nervous system effects|
|Asbestos||7 million fibers/liter (longer than 10 micrometers)||Cancer|
|Barium||2,000||Gastrointestinal disturbances, muscular weakness, hypertension|
|Beryllium||4||Bone and lung damage; possible carcinogen|
|Cadmium||5||Liver, kidney effects, bone and blood damage|
|Chromium||100||Liver, kidney, circulatory effects|
|Cyanide (as free Cyanide)||200||Neurological and thyroid effects|
|Fluoride||4 ppm||Mottling of teeth|
|Mercury (Hg)||2||Kidney effects|
|Nickel||100||Heart and liver damage|
|Nitrate||10 ppm||Methemoglobinemia (blue baby syndrome)|
|Nitrite||1 ppm||Methemoglobinemia (blue baby syndrome)|
|Selenium||50||Kidney, liver, peripheral nervous system effects|
|Thallium||2||Gastrointestinal irritation, damage to liver, kidney, intestinal, and testicular tissues, hair loss|
|Turbidity||TT||Interferes with water treatment processes|
*Fluoride, nitrate, and nitrite are expressed in parts per million (ppm).
Lead and Copper
Lead and copper are inorganic compounds that differ from other contaminants in that they are rarely found in source waters. Usually, these contaminants enter the water through the corrosion of materials in the distribution system, including household plumbing. Corrective actions, such as corrosion control and public education, are required if an action level for each contaminant is exceeded in more than 10 percent of the samples collected from household taps. The action level for lead is 15 parts per billion, and the action level for copper is 1,300 parts per billion.
Lead has been associated with impaired physical and mental development, hearing problems, and damage to the brain, nervous system, red blood cells, and kidneys.
Copper is an essential element for living organisms, including humans, andin small amountsnecessary in our diet to ensure good health. However, too much copper can cause adverse health effects, including vomiting, diarrhea, stomach cramps, and nausea. It has also been associated with liver damage and kidney disease. The human body has a natural mechanism for maintaining the proper level of copper in it. However, children under one year old have not yet developed this mechanism and, as a result, are more vulnerable to the toxic effects of copper. People with Wilson's disease also have a problem with maintaining the proper balance and should also exercise particular care in limiting exposure to copper.