How Do Pesticides Contaminate Drinking Water?

Sources of Drinking Water

• Drinking water comes from two main sources: groundwater and surface water. Examples of fresh surface water are lakes and rivers. Man-made reservoirs are also a source of drinking water. Sources of freshwater underground are also in areas called aquifers. Freshwater flows through aquifers and can be accessed by tapping into them by building wells. Water from the various sources is pumped to treatment facilities, then on to buildings and homes in urban areas.

Seepage

• Pesticides that have been applied to fields and crops can be washed away by rainfall and carried into fresh surface water areas. This happens when the pesticides have not yet bonded or degraded, allowing residual chemicals to enter freshwater sources. Pesticides can also seep into the soil and work their way into underground aquifers. The effects that pesticides have on health depends on the amount of pesticides that get into the water supply, as well as the sensitivity of the individual to the toxic chemicals and the type of pesticide used.

Direct Application and Illegal Dumping

• In some instances, pesticides may be applied directly to surface water sources to control plants or marine life considered undesirable. However, it is never recommended that these pesticides be used near drinking water facilities. The wind can also carry pesticides from their application site to contaminate drinking water sources. When homeowners dump pesticides down their drains, the pesticides can reach the drinking water supply. To avoid such contamination, always read the instructions for correct disposal or contact your state's Department of the Environment.

Common Contaminants

• Pesticides that easily dissolve in water are more likely to reach drinking water sources than those that do not. Water treatment plants that supply drinking water must disinfect the water in order to kill microbial agents that can cause disease. The Environmental Protection Agency regulates and sets standards for using these chemicals. Chlorine is an example of a disinfectant used in water treatment that can have toxic effects if too much gets into the drinking water.