Drinking Water Quality and Safety

When you turn on the tap for a glass of water, do you ever wonder about the quality or safety of that water? With drinking water, it's important to consider not just the water itself, but how that water gets to you.

The reality is, naturally pure water doesn't exist. Water is an excellent solvent, dissolving and absorbing impurities as it flows in streams, sits in lakes or filters through layers of soil and rock in the ground. Some of these substances, such as certain naturally occurring minerals, are harmless. Other naturally occurring minerals and many manmade chemicals are not. Water also contains organic matter such as dirt, leaves and microbes.

The water you drink comes from one of two sources: surface water found in lakes, rivers and reservoirs, or water found in an underground aquifer and pumped from a well. Clean, safe drinking water is essential for good health.

Drinking water quality varies from place to place, depending on the condition of its source and the treatment it receives. Sources of contaminants might be in your neighborhood or many miles away from you in the watershed, the land area drained by water as it flows into the river, lake, reservoir or aquifer.

Standards ensure safety

Public water supplies must meet quality and safety standards set by the Environmental Protection Agency (EPA) and state governments. Your local government and private water suppliers are responsible for maintaining the quality of the water that flows to your tap. They are required to test and treat the water, maintain the systems that deliver the water to consumers, and report on the water quality to the state. Every community water supplier must provide an annual report to its customers on local drinking water quality, the water's source, the contaminants found in the water, and how consumers can get involved in protecting drinking water.

The EPA has standards for more than 80 contaminants that may occur in drinking water and pose a risk to human health. These are what the EPA standards cover:

Microbes (bacteria, parasites, viruses). The EPA monitors disease-causing microbes such as Giardia lamblia and Cryptosporidium; other microbes the EPA tests for are not harmful to people but indicate that the water has not been adequately treated.
Inorganic chemicals. These can come from natural erosion or from factories and farming. Some chemicals that the EPA monitors are arsenic, cadmium, mercury, lead, nitrate/nitrite and selenium.
Organic chemicals. These can be chemicals used to treat water; chemicals such as herbicides and fungicides used in agriculture; chemicals such as insect poisons used by home owners; and chemicals from factories.
Radionuclides. These are naturally occurring radioactive minerals that may emit a form of radiation. Examples are radon, radium and uranium.
Disinfectants used in water treatment. Chlorine, chloramines and chlorine dioxide are used to disinfect public water supplies. Byproducts form when the disinfectants react with naturally occurring organic matter found in the water. Over many years, exposure to these byproducts can cause diseases or organ damage. The EPA monitors water to detect excess levels of these: trihalomethanes, haloacetic acids, bromate and chlorite.

If you need specific information about your drinking water, you can read the annual reports issued by the EPA. The reports can be found on the EPA website, http://www.epa.gov/safewater/dwh/index.html. Look under "Resources: Local Information."

Private water sources, such as wells, are not regulated by the EPA, but some state and local governments do set rules to protect well users. Unlike public drinking water systems serving many people, private sources do not have experts regularly checking the water's source and its quality. The households using this water must take special precautions to protect and maintain their drinking water source.

How is water treated?

Public water supplies are sent through treatment plants. The treatment depends on local conditions and contaminates found in the water. Chemicals called coagulants can be added to the water as it flows very slowly through tanks to make dirt and other contaminants form clumps and settle to the bottom so they can be removed. Water can be filtered to remove the smallest contaminants like viruses and Giardia. Most water suppliers add chlorine or another disinfectant to kill bacteria and other germs. If organic chemicals are present, they can be removed with activated carbon, which absorbs them. Groundwater from aquifers has been naturally filtered as it passes through layers of the earth. Water pumped from wells generally contains less organic material than surface water and may not need to go through any or all treatments.

For people who rely on wells or other private sources of water, the EPA recommends annual testing for nitrate and coliform bacteria to detect contamination problems early. Testing should be more frequent if a problem is suspected. According to the EPA, the following activities in your watershed may affect the water quality of your well, especially if you live in an area without sewers:

Recurring gastrointestinal illness: Check for coliform bacteria.
The plumbing in your house contains lead: Check for lead and copper.
Radon has been found in your home or you live in an area where radon is plentiful: Check for radon.
The pipes in your home are corroding: Check for lead.
You live in a heavily farmed area: Check for nitrate, pesticides and coliform bacteria.
You live near a coal mine or other mining operation: Check for metals.
You live near a gas drilling operation: Check for chloride, sodium, barium and strontium.
You live near a dump, landfill, factory or gas station: Check for volatile organic compounds, sulfate, chloride and metals.
Your water has an objectionable taste or smell: Check for hydrogen sulfide and metals.
Your plumbing or laundry is stained: Check for iron, copper and manganese.

For more information on safe drinking water, visit the EPA website, at http://www.epa.gov/safewater/index.html.