Protecting Public Health and the Environment.

Wastewater Collection and Treatment Systems

Wastewater systems collect and dispose of household wastewater generated from toilet use, bathing, laundry, and kitchen and cleaning activities. Any structure with running water, such as a house or office, must be connected to one of the following wastewater disposal systems:

  • Centralized systems are public sewer systems that serve established towns and cities and transport wastewater to a central location for treatment.
  • Decentralized systems do not connect to a public sewer system. Wastewater may be treated on site or may be discharged to a private treatment plant.

Centralized Systems

Large-scale public sewer systems (municipal wastewater treatment plants) are centralized systems. These systems generally serve established cities and towns and may provide treatment and disposal services for neighboring sewer districts.

Where appropriate, centralized systems are preferred to decentralized systems, as one centralized system can take the place of several decentralized systems. Centralized systems are more economical, allow for greater control, require fewer people, and produce only one discharge to monitor instead of several. However, decentralized systems can be useful, and this option should be evaluated on a case-by-case basis.

Decentralized Systems

Homes and other buildings that are not served by public sewer systems depend on decentralized septic systems to treat and dispose of wastewater. Most decentralized systems are on-site systems (wastewater is treated underground near where it is generated). On-site systems are the most common wastewater treatment system used in rural areas. These systems can be a single septic system and drainfield serving one residence or a large soil absorption system serving an entire subdivision.

Wastewater in decentralized systems can also be treated by a small, private wastewater treatment plant. These plants can have similar treatment processes and equipment as centralized systems but on a smaller scale.


DEQ State Office - Water Quality Division

1410 N. Hilton
Boise, ID 83706
(208) 373-0502

Staff Contacts

Wastewater Engineering Manager
Chas Ariss, P.E.
(208) 373-0561
chas.ariss@deq.idaho.gov

On-Site Wastewater Coordinator
Tyler Fortunati R.E.H.S
(208) 373-0140
tyler.fortunati@deq.idaho.gov

DEQ Resources

Graphic of Types of Wastewater Systems

Regional Approaches to Providing Drinking Water and Wastewater Services and Stormwater and Drainage Management Results from Statewide Listening Sessions, Final Report (January 2007)

Wastewater Security Fact Sheet (August 2006)

A Homeowner's Guide to Septic Systems (January 2001)

A Guide to Community Septic Systems (February 2002)

More Information

Primer for Municipal Wastwater Treatment Systems

Related Pages

On-Site Wastewater Systems (Septic Systems)