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 think about not just the water itself, but how that water gets to you.

The reality is, naturally pure water doesn't exist. Water is very good at 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 are harmless. This includes some naturally occurring minerals. But other naturally occurring minerals and many artificial 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
• Water found in an underground aquifer and pumped from a well

Clean, safe drinking water is important for good health.

Drinking water quality differs from place to place. It depends on the condition of its source and the treatment it gets. Sources of contaminants might be in your neighborhood. Or they may be many miles away from you in the watershed. The watershed is the land area drained by water as it flows into the river, lake, reservoir, or aquifer.

Public water supplies must meet quality and safety standards set by the EPA and state governments. Your local government and private water suppliers are responsible for managing the quality of the water that flows to your tap. They are required to test and treat the water. They must also maintain the systems that deliver the water to consumers. They report on the water quality to the state. Every community water supplier must provide a report to its customers every year on local drinking water quality. The report also must include the water's source, the contaminants found in the water, and how consumers can help protect drinking water. This is called a Consumer Confidence Report.

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 watches for disease-causing microbes. Other microbes the EPA tests for are not harmful to people. But they show that the water has not been correctly 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 or nitrite, and selenium. Many communities add fluoride to their drinking water to help prevent tooth decay.
• Organic chemicals. These can be chemicals used to treat water. They can also be chemicals such as herbicides and fungicides used in agriculture. Or they can be chemicals such as insect poisons used by homeowners and chemicals from factories or underground drilling (known as "fracking"). Many of these can mimic the effects of estrogen and other hormones if ingested in significant amounts.
• Radionuclides. These are naturally occurring radioactive minerals that may give off a form of radiation. Examples include 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 find extra levels of these: trihalomethanes, haloacetic acids, bromate, and chlorite.

If you need exact information about your drinking water, you can read the annual reports from the EPA. The reports can be found at the EPA. Watch for warnings telling you to boil water before you drink it.

The EPA does not regulate private water sources such as wells. But some state and local governments do set rules to protect well users. Unlike public water systems, private water sources don't have experts regularly checking the water's source and its quality. Households using private water must take special safety steps to protect and maintain their drinking water source. They should have their well tested on a regular basis. They should always test it after any local flooding or construction near the well. They should also think about getting a personal water treatment system.

Public water supplies are sent through treatment plants. The treatment depends on local conditions and impurities in the water. Chemicals called coagulants can be added to the water as it flows very slowly through tanks. This will make dirt and other impurities form clumps. These clumps settle to the bottom so they can be removed. Water can be filtered to remove the smallest impurities. Most water suppliers add chlorine or another disinfectant to kill bacteria and other germs. Any organic chemicals can be removed with activated carbon. This soaks them up. 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. Well water may not need to go through any or all treatments.

For people who depend on wells or other private water sources, the EPA advises annual testing for nitrate, pH (acidity and alkalinity), total dissolved solids, and coliform bacteria. This can help to find problems early. Test more often if you think there is a problem. According to the EPA, certain activities in your watershed may affect the water quality of your well. This is even more likely if you live in an area without sewers. These activities include:

• Digestive illness that keeps coming back. 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 common. Check for radon.
• The pipes in your home are corroding. Check for lead.
• You live in a heavily farmed area or near a concentrated animal feeding operation. 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 unpleasant taste or smell. Check for hydrogen sulfide and metals.
• Your plumbing or laundry is stained. Check for iron, copper, and manganese.

Please note: If you have not used your tap water for some time, flush out the system of any microbes that may be present, such as Legionella.

For more information on safe drinking water, visit the EPA.

Bottled water is a popular way to get drinking water in the U.S. You may choose bottled water because you like how it tastes. Or you may have health concerns about your tap water. You may also choose bottled water instead of other kinds of drinks.

The FDA sets standards for bottled water in the U.S. The FDA bases its standards on the standards set by the EPA for drinking water.

You can find out more about the bottled water you drink by looking at the label. The label may tell you about the treatment process used. The label may also have a toll-free number to call or a website to visit for more information. Plastic bottles often have a number on the bottom that indicates if they contain certain substances that, for instance, should not be warmed in a microwave.

This treatment information is especially important if you have a weakened immune system. Check that the bottled water you drink takes steps to protect against the parasite cryptosporidium. This parasite can cause serious illness. Treatments that can block this parasite include:

• Reverse osmosis
• Distillation
• Filtration with a 1 micron filter