Septic System Basics

In areas where public sewer is not available, homeowners must have septic systems (also known as sewage systems) installed on their property that will treat wastewater coming from their home.

All facilities such as toilets, sinks, bathtubs, showers, washing machines, dishwashers, or anything else that generates sewage MUST be connected to the septic system.

Footing drains, roof drains, storm water pipes, and water softening waste should NOT be connected to septic systems. These items should discharge away from the drainfield area, and in a manner that does not impact neighboring property. Also, water softener wastewater should not discharge near wells or surface water.

On-site septic systems must be designed according to Washtenaw County standards, and must be inspected and approved by a Sanitarian (health inspector). Septic systems are different from municipal sewers because they often have a limited life expectancy, which can be drastically reduced if the system is improperly used or not maintained. (See Maintaining Your Septic System.)

Septic System

Typical Septic System Components

Pipe from House

All of your household wastewater exits your home through a pipe that flows into the septic tank.

Septic Tank

The septic tank is a buried, watertight container that holds wastewater long enough for solids to settle out (sludge), and oil, grease, and hair to float to the surface (scum). Solid materials begin to decompose, and anaerobic breakdown of bacteria takes place. Most newer septic systems have two septic tanks. Compartments and a baffle or outlet tee in the septic tank prevents the sludge and scum from leaving the tank and entering the drainfield. Septic tanks need to be pumped every 3 to 5 years to remove the scum and sludge.

Septic System Basics


Every time new wastewater enters the septic tank, the same amount of wastewater (or effluent) exits the tank and is pushed into the drainfield. If the drainfield is overloaded with too much liquid, it will flood. If this happens, the wastewater won't be treated properly and sewage may flow to the surface of the ground or back up into the house. A reserve drainfield is an area on your property suitable for a new drainfield system if your current drainfield fails.


Septic tank wastewater flows to the drainfield, where it percolates into the soil and is filtered. Natural processes remove most of the contaminants in the wastewater before it eventually reaches groundwater. Aerobic breakdown of bacteria also occurs in the soil. Soil that allows for percolation, or drainage, is necessary for successful wastewater treatment.

Signs of Septic System Problems

A failed septic system is a health hazard to you, your family, and your neighbors. Call the Washtenaw County Environmental Health Division at 734-222-3800 at the first signs of failure, and we will assist you in your efforts to remedy the situation.

If a sewage system fails, obvious sign appear:

  • Toilets back up; drains won't drain.
  • Excessive moisture or waste water surfaces over the drainfield.
  • Foul odors come from the drainfield or septic tank.

See Maintaining Your Septic System for tips on keeping your system functioning properly.