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Water: Septic (Onsite / Decentralized) Systems

The Basics

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What Is a Septic System?  

Common in rural areas without centralized sewer systems, septic systems are underground wastewater treatment structures that use a combination of nature and time-tested technology to treat wastewater from household plumbing produced by bathrooms, kitchen drains, and laundry.  

How Does A Septic System Work?  

A typical septic system consists of a septic tank and a drainfield, or soil absorption field. Below is a brief overview of how septic systems work. For an animated, interactive model of a household septic system, visit the Guadalupe-Blanco River Authority website on how a septic system works! Exit EPA Disclaimer
  1. All water runs out of your house from one main drainage pipe into a septic tank.

  2. The septic tank is a buried, water-tight container usually made of concrete, fiberglass, or polyethylene. Its job is to hold the wastewater long enough to allow solids to settle down to the bottom (forming sludge), while the oil and grease floats to the top (as scum).

    Compartments and a T-shaped outlet prevent the sludge and scum from leaving the tank and traveling into the drainfield area. 

  3. The liquid wastewater (effluent) then exits the tank into the drainfield. If the drainfield is overloaded with too much liquid, it will flood, causing sewage to flow to the ground surface or create backups in toilets and sinks. 

  4. Finally, the wastewater percolates into the soil, naturally removing harmful coliform bacteria, viruses, and nutrients.

Do You Have a Septic System? 

You may already know you have a septic system. If you don’t know, here are tell-tale signs that you probably do:
  • You use well water.
  • The waterline coming into your home doesn’t have a meter.
  • You show a “$0.00 Sewer Amount Charged” on your water bill.
  • Your neighbors have a septic system.

How To Find Your Septic System 

Once you’ve determined that you have a septic system, you can find it by:Septic Tank Pipe
  • Looking on your home’s “as built” drawing.
  • Checking your yard for lids and manhole covers.
  • Contacting a septic inspector/pumper to help you locate it. 

Failure symptoms: Mind the signs! 

A foul odor isn’t always the first sign of a malfunctioning septic system. Call a septic professional if you notice any of the following:
  • Wastewater backing up into household drains.
  • Bright green, spongy grass on the drainfield, even during dry weather.
  • Pooling water or muddy soil around your septic system or in your basement.
  • A strong odor around the septic tank and drainfield.
  • Mind the signs of a failing system. 
One call to a septic professional could save you thousands of dollars! Homeowners can contact their local or state health department for more information about onsite wastewater practices in their community at Contacts

Looking to Launch a Local Outreach Campaign?
  • Check out the SepticSmart Outreach Toolkit!Toolbox

    Government officials, industry professionals, environmental groups, and other local organizations can access ready-to-use educational materials, case studies, and more.

SepticSmart LogoContact SepticSmart Staff: 
Phone: 208/378-5626

E-mail: decentralized@epa.gov

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