Department of
Environmental Quality

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 some sort of wastewater disposal system. There are generally two types of systems:

• Centralized systems are "public sewer systems" and usually serve established towns and cities and transport wastewater to a central location for treatment.
  
• Decentralized systems are systems that do not connect to a public sewer system. They may treat wastewater on-site or may discharge to a private treatment plant.
  

Centralized Systems

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

Where appropriate, centralized systems are generally preferred to decentralized systems, as one centralized system can take the place of several decentralized systems. This makes centralized systems more economical, allows for greater control, requires fewer people, and produces only one discharge to monitor instead of several. However, there are good reasons for use of decentralized systems and options 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 as small as a single septic system and drainfield serving one residence or as large as a large soil absorption system serving an entire subdivision.

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