Coliform bacteria are a closely related group of bacteria species that live in the intestinal tracts of animals and are generally not harmful to human health. A few types of bacteria within the total coliform group, most notably E. coli, can cause serious illness.

Coliform bacteria are common in the environment and are easily identified during routine water testing; therefore, they are frequently used as indicators that a water supply may be contaminated. If coliform bacteria show up in a water sample, it is possible that disease-causing bacteria, viruses, and parasites are also present.

E. coli (short for Escherichia coli) is a specific type of fecal coliform bacteria that is only found in waste from animals or humans. The presence of E. coli is a strong indication that human sewage or animal waste has contaminated the water raising the risk of gastrointestinal illnesses.

Arsenic is a naturally occurring element that can enter drinking water supplies from natural deposits in the earth or from agricultural and industrial practices. While arsenic is not in common use today, it was once an ingredient in some pesticides, and residues remain from past use and improper disposal.

The health risks associated with arsenic result from low-level exposure over a long period of time. Some people who drink water containing high levels of arsenic for many years could experience skin damage, problems with their nervous or circulatory systems, and may have an increased risk of developing some forms of cancer.

The maximum contaminant level (MCL) for public water systems is 10.0 micrograms per liter (ug/L, aka. parts per billion or ppb), however any level of arsenic may be harmful. 

Nitrate poses a health concern for young children and infants in particular. Infants under six months of age who drink water containing nitrate in excess of the maximum contaminant level (MCL) could become seriously ill and, if untreated, may die. Symptoms include shortness of breath and blue baby syndrome.

The maximum contaminant level (MCL) for nitrate is 10.0 milligrams per liter (mg/L).

Nitrite is a form of nitrogen that is readily oxydized (combines with oxygen) to form nitrate. Nitrate poses a health concern for young children and infants in particular. Infants under six months of age who drink water containing nitrate at high levels could become seriously ill and, if untreated, may die. Symptoms include shortness of breath and blue baby syndrome.

The maximum contaminant level (MCL) for nitrite is 1.0 milligrams per liter (mg/L).

Lead exists throughout our physical environment. We are exposed to very small amounts each day, usually with no bad health effects. Groundwater in Minnesota usually does not contain detectable levels of lead. However, the pipes and other components (such as faucets, valves, or fittings) in household plumbing may contain lead. If they do, lead  may dissolve into the water. The longer the water stands idle in the plumbing pipes and components, the more lead that can dissolve into the water.

The maximum contaminant level (MCL) for public water systems is 10.0 micrograms per liter (ug/L, aka. parts per billion or ppb), however there is no safe level of lead in drinking water.

Copper is a metal that is found naturally in rock formations. Your body needs some copper to stay healthy, but too much is harmful. It is used to make many products, including parts for plumbing systems. Copper can get into your drinking water as the water passes through your household plumbing system if it contains copper piping or parts.

The maximum contaminant level (MCL) for public water systems is 1,300 micrograms per liter (ug/L, aka. parts per billion or ppb).

Manganese occurs naturally in rocks and soil across Minnesota and is often found in Minnesota ground and surface water. Your body needs some manganese to stay healthy, but too much can be harmful. The Minnesota Department of Health (MDH) developed guidance values to keep your household drinking water safe. Because these are guidance values, public water systems are not required to meet these values, and some do not.

For infants who drink tap water, or drink formula made with tap water, a safe level of manganese in your water is 0.100 milligrams per liter (mg/L) or less.

For adults and children over the age of one, a safe level of manganese in your water is 0.300 milligrams per liter (mg/L) or less. 

Iron can be a troublesome chemical in water supplies. Making up at least 5 percent of the earth’s crust, iron is one of the earth’s most plentiful resources. As rainwater infiltrates the soil and underlying geologic formations, it dissolves iron, causing it to seep into aquifers that serve as sources of groundwater for wells. Although present in drinking water, iron is seldom found at concentrations greater than 10 milligrams per liter (mg/L) or 10 parts per million. However, concentrations of iron as low as 0.3 mg/L will leave reddish brown stains on fixtures, tableware and laundry that are very hard to remove.

Hard water requires more soap and synthetic detergents for home laundry and washing and contributes to scaling in boilers and industrial equipment. Hardness is caused by compounds of calcium and magnesium, and by a variety of other minerals. Water is an excellent solvent and readily dissolves minerals. As water moves through soil and rock, it dissolves very small amounts of minerals and holds them in solution. Calcium and magnesium dissolved in water are the two most common minerals that make water “hard.”

Water is a good solvent and picks up impurities easily. Pure water — tasteless, colorless, and odorless — is often called the universal solvent. “Dissolved solids” refer to any minerals, salts, metals, cations or anions dissolved in water. Total dissolved solids (TDS) comprise inorganic salts (calcium, magnesium, potassium, sodium, bicarbonates, chlorides and sulfates) and some small amounts of organic matter that are dissolved in water.

Tannins are natural organic matter that can result from nature’s fermentation process as water passes through the ground in peaty areas or through levels of decaying vegetation. Tannins are typically found in shallow wells, in swampy or marshy areas as well as coastal areas. Common signs of tannins include yellow or tea-colored water, yellow or brown staining on toilet fixtures, and yellow or brown staining on laundry.

pH is a measure of how acidic/basic water is. The range goes from 0 – 14, with 7 being neutral. In general, water with a pH lower than 7 is considered acidic, and with a pH greater than 7 is considered basic. The normal range for pH in well water is 6.0 to 8.5

Iron bacteria are small living organisms that naturally occur in soil, shallow groundwater, and surface waters. These bacteria combine iron (or manganese) and oxygen to form deposits of “rust,” bacterial cells, and a slimy material that sticks the bacteria to well pipes, pumps, and plumbing fixtures.

Iron bacteria are not known to cause disease. However, they can create conditions where other disease-causing organisms may grow. They can also affect how much water the well produces and may cause clogging issues.

Hydrogen sulfide gas can give water a “rotten egg” taste or odor. This gas can occur in wells anywhere and be naturally occurring—a result of decay and chemical reactions with soil and rocks, or can be produced by certain sulfur bacteria in the groundwater, well, or plumbing system.

Sulfur bacteria produce a slime and can help other bacteria grow, such as iron bacteria. The slime can clog wells, plumbing, and irrigation systems. While sulfur bacteria are not harmful, hydrogen sulfide gas in the air can be harmful at high levels.