The United States has one of the safest water supplies in the world. However, drinking water quality varies depending on the condition of the source water from which it is drawn and the treatment it receives. In nature, all water contains some impurities as the flowing water dissolves or absorbs the substances that it touches. Some of the contaminants come from erosion of natural rock formations. Other contaminants are substances from factories, farmlands, homes and yards. Local water quality reports provide a list of contaminants in drinking water with the levels at which they were found, and also the actual or likely source of each contaminant.
Even though Environmental Protection Agency (EPA) does not regulate private wells, it has recommendations for their owners. Every community water supplier must provide a consumer confidence annual report to its customers. The report provides information on local drinking water quality, including the source and the contaminants found in the water.
Some ground water systems have established protection programs to prevent substances from contaminating their wells. Some surface water systems protect the watershed around their reservoir to prevent contamination. The states and water suppliers systematically assess every source of drinking water to identify potential sources of contaminants. People in large cities frequently drink water that comes from surface water sources, such as lakes, rivers, and reservoirs. In rural areas, people are more likely to drink ground water pumped from wells that tap into aquifers or natural reservoirs under the earth’s surface.
The Safe Drinking Water Act gives the EPA the responsibility for setting national drinking water standards for public water systems. However, water from private wells is not subject to Federal Regulations. States and the EPA provide technical assistance to water suppliers and are authorized to take legal action against systems that do not provide water that meets state and EPA standards. The EPA has set standards for more than 80 contaminants that may occur in drinking water posing a risk to human health. The contaminants are divided into two groups according to the health effects that they cause, such as acute effects and chronic effects. Acute effects occur within hours or days of the time that a person consumes a contaminant. People can suffer acute health effects from almost any contaminant when exposed to extraordinarily high levels. Microbes, such as bacteria and viruses, are the contaminants in drinking water with the greatest chance of reaching levels high enough to cause acute health effects. Chronic effects occur after people consume a contaminant at levels over EPA safety standards for many years. Drinking water contaminants that can have chronic effects are chemicals, radionuclides and minerals. Chronic effects of drinking water contaminants include cancer, liver or kidney problems, or reproductive difficulties.
Untreated water from a river or reservoir often contains dirt, organic matter, and trace amounts of certain contaminants. Usually, water suppliers add coagulants to the water at a treatment plant. The coagulants act on the water forming clumps of dirt and other contaminants that settle to the bottom of tanks. The smallest contaminants like viruses and Giardia are usually removed through a filter. Ground water is naturally filtered as it passes through layers of the earth into underground reservoirs known as aquifers. Water pumped from wells generally contains less organic material than surface water and may not need to go through all of the treatments. Disinfection is the most common drinking water treatment. Water suppliers add chlorine or another disinfectant to kill bacteria and other germs.
Drinking water suppliers are required to monitor and test their water many times, to determine whether and how the water needs to be treated, and effectiveness of the treatment process. A system is violating regulations, and is subject to fines and other penalties, if the system fails to monitor for a contaminant. When a water system violates a drinking water regulation, it is required to notify the people who drink its water about the violation. Moreover, each water suppliers’ annual water quality report must include a summary of all the violations that occurred during the previous year.