The Treatment Path

Follow a drop of water from the source through the treatment process and find-out the steps it follows before it flows from your faucet.

Water may be treated differently in different communities, depending on the quality of the water that enters the treatment plant. Groundwater typically requires less treatment than water from lakes, rivers and streams.

In the U.S., governments set standards or guidelines for drinking water. When water leaves a treatment plant it is as clean or cleaner than required.

INTAKE

Large things such as logs, sticks, fish and plants are screened-out as the water is drawn into the treatment plant from a river, lake or other surface source. If the source is groundwater, the screening is done by nature as the water travels under the surface of the earth.

PRE-TREATMENT

Chlorine and other chemicals, such as alum or lime, are added to the water to help remove impurities and destroy bad taste or odor. Sometimes chemicals are included to remove excess minerals that make the water "hard" or cause rust to form.

MIXING

The water is mixed rapidly to distribute the chemicals evenly.

COAGULATION and FLOCCULATION

The water is sent into a large basin where the chemicals cling to the impurities in the water (coagulation) causing them to form larger, heavier particles called floc. These then settle to the bottom of the basin so the chemicals and impurities can be removed.

FILTRATION

From the basin, where the floc settles (sedimentation basin), the water continues on its trip through the filters. Layers of sand, gravel and sometimes hard coal (anthracite) are used to remove any other impurities that are left in the water. Another filter may be used to remove toxic organic substances. As the water passes through this layer, certain impurities stick to the filter material. This is called adsorption.

CHLORINATION

Now that everything has been removed from the water, a small amount of chlorine is added to keep the water from developing bacteria. The amount added is carefully measured to be the lowest amount needed to keep the water free of germs. Some treatment facilities also add fluoride.

DISTRIBUTION

The water now travels through large pipes (called mains) to where it will be used, or it may be stored in a reservoir or tank.