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Drinking Water

Drinking water can come from both surface water and ground water. The water cycle begins with rainwater and snow melt that gathers in lakes and rivers which interact with ground water.

As water flows in streams, sits in lakes, and filters through layers of soil and rock in the ground, it dissolves or absorbs the substances that it touches. Some of these substances are harmless. In fact, some people prefer mineral water precisely because minerals give it an appealing taste. However, at certain levels, minerals, just like man-made chemicals, are considered contaminants that can make water unpalatable or even unsafe. Some contaminants come from erosion of natural rock formations. Other contaminants are substances discharged from factories, applied to farmlands, or used by consumers in their homes and yards. Sources of contaminants might be in your neighborhood or might be many miles away.

Graphic depicting the water cycle

A clean, constant supply of drinking water is essential to every community. Large-scale water supply systems tend to rely on surface water sources. Sometimes these sources are close to the community. Other times, drinking water suppliers get their water from sources many miles away. In either case, when you think about where your drinking water comes from, it’s important to consider not just the part of the river or lake that you can see, but the entire watershed. The watershed is the land area over which water flows into the river, lake, or reservoir. 

For small systems and rural areas, people are more likely to drink ground water that was pumped from a well. These wells tap into aquifers—the natural reservoirs under the earth’s surface—that may be only a few miles wide, or may span the borders of many states. As with surface water, it is important to remember that activities many miles away from you may affect the quality of ground water.

Water systems come in all shapes and sizes, and no two are exactly the same. They may be publicly or privately owned and maintained. While their design may vary, they all share the same goal providing safe, reliable drinking water to the communities they serve. To do this, water systems must treat their water. The types of treatment provided by a specific system vary depending on the size of the system, whether they use ground water or surface water, and the quality of the source water.

Water Treatment

The amount and type of treatment applied by a system varies with the source type and quality. Water suppliers use a variety of treatment processes to remove contaminants from drinking water. The most commonly used processes include filtration, flocculation and sedimentation, and disinfection for surface water. Some treatment trains also include ion exchange and adsorption. Water utilities select a combination of treatment processes most appropriate to treat the contaminants found in the raw water used by the system.

Water systems monitor for a wide variety of contaminants to verify that the water they provide to the public meets all federal and state standards. The major classes of contaminants include volatile organic compounds (VOCs), synthetic organic compounds (SOCs), inorganic compounds (IOCs), radionuclides, and microbial organisms (including bacteria). Testing for these contaminants takes place on varying schedules and at different locations throughout the water system. Water systems also monitor for a number of contaminants that are currently not regulated. This monitoring data provides the basis for identifying contaminants to be regulated in the future.

An underground network of pipes typically delivers drinking water to the homes and businesses served by the water system. Small systems serving just a handful of households may be relatively simple. Large water systems can be extremely complex sometimes with thousands of miles of piping serving millions of people. Although water may be safe when leaving the water treatment plant it is important to ensure that this water does not become contaminated in the distribution system because of such things as water main breaks, pressure problems, or growth of microorganisms. Much of the existing drinking water infrastructure was built many years ago.

Who is responsible for drinking water treatment?

The Safe Drinking Water Act gives the Environmental Protection Agency (EPA) the responsibility for setting national drinking water standards that protect the health of the millions of people who get their water from public water systems. Those who get their drinking water from private wells are not subject to federal regulations. Since 1974, EPA has set national standards for dozens of contaminants that may occur in drinking water. While EPA and state governments set and enforce standards, local governments and private water suppliers have direct responsibility for the quality of the water that flows to your tap. Water systems test and treat their water, maintain the distribution systems that deliver the water to consumers, and report on their water quality to the state. States and EPA provide technical assistance to water suppliers and can take legal action against systems that fail to provide water that meets state and EPA standards.

Did you know?

  • Water is the only substance found on earth in three forms; solid, liquid, and gas.

  • No new water is produced, it is recycled over and over.

  • Every living thing on earth depends on water, in varying degrees, for survival.

  • A person can live more than a month without food, but only a few days, depending on conditions, without water.

  • Up to 60% of the human body is water, the brain is composed of 70% water, and the lungs are nearly 90% water.

  • 70% of a chicken, 87% of a pineapple, and 94% of a tomato is water. 

  • Water regulates the earth’s temperature. It also regulates the temperature of the human body, carries nutrients and oxygen to cells, cushions joints, protects organs and tissues, and removes wastes. 

  • It is possible for people today to drink water that was part of the dinosaur era.