Wastewater is spent or used water, such as from households and businesses, that contains enough harmful material to damage the water's quality. Every building with running water generates some sort of wastewater. Wastewater may contain contaminants such as oil, dirt, human waste, and chemicals. Untreated wastewater can cause serious harm to the environment and threaten human health. Proper management and disposal of wastewater is essential to protect public health and Idaho's water quality.

Any structure or facility that generates wastewater must dispose of it through some sort of wastewater treatment and disposal system. There are generally two types of systems: centralized and decentralized. 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. View graphic of types of systems. 

Once wastewater has been treated, various options exist for its "disposal," including discharging to surface waters and land application.

Centralized wastewater systems (city sewer systems) connect homes, businesses, and industry directly to a wastewater treatment plant where it is treated before being discharged into the environment. More on centralized systems. 

Municipal wastewater treatment plants need a National Pollutant Discharge Elimination System (NPDES) permit to discharge treated wastewater into waters of the Unites States. The permit includes provisions relating to biosolids and may also specify pretreatment requirements for industries that discharge their wastewater to the wastewater treatment plant.

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). 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.  More on on-site decentralized systems. 

Once wastewater has been treated, it is "disposed" of by re-introducing it to the environment. The three main methods of disposing of treated wastewater effluent are surface water discharge, subsurface discharge, and land application for beneficial use.

Subsurface discharge occurs on-site where wastewater is treated by discharging septic tank effluent underground where it leaches through a drainfield.  Read more about on-site treatment systems. 

In some situations, treated wastewater can be applied to land for irrigation. The small amount of pollutants remaining in the wastewater after treatment are absorbed by the crop or are assimilated into the soil structure.

Depending on the contaminants, the water may require pretreatment prior to discharge to meet water quality standards. DEQ issues permits for facilities treating wastewater and sludge through this method. More. 

Industrial, municipal, and other point sources of pollution that discharge wastewater directly to surface waters are required to obtain NPDES permits that limit the amount of pollution that may be discharged into surface waters. (A point source is a source of pollution that comes from a discrete pipe or other "point").

In Idaho, the NPDES permit program is administered by the U.S. Environmental Protection Agency (EPA), which means that EPA is responsible for issuing and enforcing all NPDES permits in Idaho. The state's role in this process is to certify that NPDES-permitted projects comply with state water quality standards. 

An NPDES permit generally allows a facility to discharge a specific amount of a pollutant into a receiving water under certain conditions; a permit may allow a facility to dispose or re-use its by-products in other ways as well. Wastewater treatment plants, aquaculture facilities, concentrated animal feeding operations, industrial sites, and certain facilities or areas (e.g., construction sites and municipalities) that discharge storm water are required to obtain NPDES permits. More. 

Pollutant trading is a voluntary, business-like way of helping to improve water quality by controlling wastewater discharges to surface waters in a cost-effective manner. The program generally involves one facility facing relatively high pollutant reduction costs paying another facility (with lower pollution reduction costs) to reduce its pollution to allow the first facility to discharge more than its share. Thus, the level of pollutants discharged in wastewater to a specific body of water stays the same (or is reduced) and both businesses are better off, financially, as a result of the trade. More. 

Conserving water and minimizing contaminants in wastewater are good management strategies that can save businesses money while protecting the environment. The following tips may help facilities conserve water, protect water quality, and save money:

• Prevent accidental contamination of wastewater by properly storing and labeling chemicals and wastes. Store chemicals and wastes away from drains. Use secondary containment measures around chemical and waste containers.
• Clean with a mop, broom, or vacuum instead of hosing down floors, walkways, and parking areas.
• Explore equipment or processes that allow for water reuse. Water reuse includes using spent process water for pre-rinsing or applying non-hazardous water to land for irrigation. 
• Recycle water. Water recycling equipment treats water so that it can be reused. Many are closed loop systems that help conserve water as well.
• Substitute less hazardous chemicals for processes and cleaning to minimize contaminants in wastewater.

Rules for the Reclamation and Reuse of Municipal and Industrial Wastewater (IDAPA 58.01.17) (pdf on Department of Administration Web site)