A septic system is used to treat and dispose of wastewater, usually from homes, businesses, and commercial buildings that are close together. Septic systems are widely used in rural and other areas where homes do not have access to a local wastewater treatment facility. The typical septic system includes a pipe from a home’s plumbing system; a septic tank, where bacteria digest organic matter and solids separate from the wastewater; a drain or leach field; and soil. Wastewater liquid flows from the tank to pipes buried in the drain field. The soil in the drain field filters the water, and then the soil surrounding the drainfield filters the water again. Solids remain in the tank and are regularly pumped out by septic system maintenance companies. A properly functioning septic system returns clean, safe water to the environment through the soil. 

Wastewater can include nitrogen, phosphorus, bacteria, and viruses. A failing septic system can contaminate groundwater and sources of drinking water with untreated sewage, causing disease and infection in people and animals. Foul odors from failing septic systems can be nauseating. Untreated sewage can contaminate lakes, streams, reservoirs, and rivers. A failing septic system can contaminate sensitive coastal waters, increase algae blooms, lower oxygen levels in the water, and contaminate shellfish beds and beaches. 

If materials such as chemicals, oil, gas, pesticides, or paints enter a septic system, they can harm the environment. These toxic liquids should never be poured down the drain. Flies and mosquitoes that can spread disease may breed in wet areas where wastewater reaches the surface. 

Septic systems protect the environment and public health when they are properly sited, constructed, and maintained. State and local governments regulate septic systems.

This description is based on the information found in the Web links listed with this topic.

Web Links from MedlinePlus (National Library of Medicine)
Drinking Water
E. Coli Infections
Giardia Infections
Hepatitis A
Parasitic Diseases
Water Pollution

More Links
Groundwater Protection and Your Septic System (National Small Flows Clearinghouse) (PDF — 287 KB)
Homeowner's Guide to Septic Systems (Environmental Protection Agency) (PDF — 1.62 MB)
Managing Septic Systems to Prevent Contamination of Drinking Water (Environmental Protection Agency) (PDF — 132 KB)
On-Site Wastewater Treatment (Centers for Disease Control and Prevention)
Septic (Onsite/Decentralized) Systems (Environmental Protection Agency)
Septic Systems - What to Do After the Flood (Environmental Protection Agency)
Septic Tank Servicers and Sewer Pipe Cleaners. Haz-Map (National Library of Medicine)

Last Updated: December 17, 2012