An illustration of example sources including homes, businesses, schools, and industries


Wastewater is the used water that flows from communities.

While most people think of wastewater as merely sanitary sewage, wastewater actually comes from many sources, including homes, businesses, schools, and industries. This flow includes water from toilets, showers, sinks, dishwashers, laundry machines, car washes, hospitals, and food processing operations, and this is just scratching the surface.

Influent at HITE
Samples of water

As its name implies, “wastewater” is mostly water.

In fact, wastewater typically averages 99.94% water by weight; only a small 0.06% is actually waste material. So what makes up this other small percentage?

Waste material is either dissolved or suspended in the water, and it too can come in many forms. Aside from the most obvious human waste, our daily activities contribute many other water contaminants, including food particles, paper products, dirt, oil and grease, proteins, organic materials such as sugars, inorganic materials such as salts, personal care products, pharmaceuticals, cleaning solutions, and hundreds of other chemicals.

Concentrations of these substances are usually referred to in milligrams of pollutants per liter of water (mg/l) or parts per million (ppm). To put these terms in perspective, one ppm is equivalent to one minute of time in 1.9 years or one inch in 16 miles. These statistics emphasize that wastewater treatment processes are designed to remove a few milligrams per liter of a pollutant, which is like sifting through a haystack to remove a tiny needle. However, the balance of nature depends on the ability to do just that—and our wastewater treatment plants accomplish this continuously 24 hours a day, 365 days a year.

Learn more about Metro’s facilities


Water recovery entities that are owned and operated by a governmental agency like Metro are called publicly owned treatment works (POTWs) under state and federal Clean Water laws.

POTWs like Metro are designed to treat residential sewage (domestic waste, which come from household toilets, showers, dishwashers, and sinks) and not the types of contaminants that are present in wastewater from commercial and industrial businesses, including waste haulers. Discharges from businesses can harm the equipment and operations of a POTW and the downstream water bodies. The sources of wastewater that a POTW receives for treatment depend upon the specific service area that is served by the POTW.

Robert W. Hite Treatment Facility (RWHTF)

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flow from residences

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flow from commercial and industrial businesses.

Northern Treatment Plant (NTP)

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flow from residences

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flow from commercial and industrial businesses.

“Commercial” dischargers include:

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  • waste haulers who collect food and septage waste
  • warehouses
  • automotive repair shops
  • car washes
  • print shops
  • medical offices
  • shopping malls and beauty shops

“Industrial” dischargers are generally facilities:

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  • that involve some type of manufacturing operations
  • which conduct activities that support manufacturing facilities

Of the 30.6% of non-residential flow into the RWHTF, only 1.4% of the flow is considered to be “industrial.” Currently, NTP does not receive any flows that are considered to be “industrial.”

Industrial Pretreatment Program (IPP)

To minimize the possibility that contaminants from industrial and commercial discharges will interfere with the operation of POTWs, the EPA created the National Pretreatment Program, which regulates the non-residential discharges to POTWs.

Metro’s discharge permits require that we implement an EPA-approved IPP across our entire 715-square mile service area to control the discharges from businesses. The EPA approved Metro’s IPP on August 25, 1986.

POTWs with an EPA-approved IPP directly regulate the commercial and industrial businesses within the POTW’s service area. The regulations that apply to the businesses within Metro’s service area are found in Sections 5, 6, and 10 of Metro’s Rules and Regulations and in the federal General Pretreatment Regulations of the National Pretreatment Program. Under its IPP, Metro does not have authority to regulate dischargers other than businesses – so for both RWHTF and NTP, Metro does not have authority to regulate any of the domestic discharges from residences.

The EPA oversees Metro’s ongoing IPP implementation by reviewing the annual reports that we submit and by conducting on-site audits.

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Site visit of industrial user Rocky Mountain Bottling

A key aspect of Metro’s IPP involves our IPP team members working with the businesses who discharge to our connectors. This includes several different types of activities:

  • Identifying and maintaining a list of businesses
  • Inspecting businesses
  • Evaluating business operations and waste streams
  • Notifying businesses of applicable requirements, which could include obtaining a Metro IPP permit and/or Implementing best management practices (BMPs)
  • Collecting samples
  • Reviewing data and reports
  • Evaluating compliance
  • Providing compliance assistance to businesses
  • Taking formal enforcement action where necessary

Hauled Waste Program (HWP)

Like all POTWs with an EPA approved IPP, Metro regulates waste haulers through its IPP, under special requirements called the HWP. 

Hauled Waste

Under its HWP, Metro only allows waste haulers to discharge septage from port-a-potties and septic tanks and grease from restaurants. Currently, Metro only has the physical infrastructure in place to receive hauled waste at the RWHTF. Every spring, Metro also recognizes businesses who meet their industrial discharge requirements and demonstrate a commitment to environmental excellence for prior years.

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