Drinking Water Standards for Contaminants: Microbiological, Radiological, and Inorganic Contaminants Fact Sheet - EH: Minnesota Department of Health

Environmental Protection Agency Safe Drinking Water Act Standards:
Microbiological, Radiological, and Inorganic Contaminants

Safe Drinking Water Act

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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” contaminants—based on established state health standards and an assessment of the risks they pose—the 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.

MCL—Maximum Contaminant Level
ppb—parts per billion
ppm—parts per million
TT—Treatment Technique

Microbiological Contaminants

Microbiological organisms—including bacteria, protozoa, and viruses—are 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.

Radiological Contaminants

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.

Radiological Contaminant
Potential Health Effects
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 Contaminants

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
Antimony 6 Diarrhea
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, and—in small amounts—necessary 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.

Updated Monday, January 15, 2018 at 09:52AM