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Wastewater removal and treatment is critical to protect public health. Wastewater treatment processes improve water quality by reducing toxins that cause harm to humans and pollute rivers, lakes, and oceans. Wastewater enters the treatment system from households, business, and industry through public sewer lines and, in many places across the country, stormwater drains.

Wastewater treatment is typically overseen by a community utility or public works department that ensures water quality standards are met before the treated water is discharged back into the environment. In most localities, all publicly-supplied water is treated to meet federal drinking water standards, regardless of whether it will be used for drinking. Nearly 240 million Americans – 76% of the population – rely on the nation’s 14,748 treatment plants for wastewater sanitation. By 2032 it is expected that 56 million more people will connect to centralized treatment plants, rather than private septic systems – a 23% increase in demand. In the U.S., there are over 800,000 miles of public sewers and 500,000 miles of private lateral sewers connecting private property to public sewer lines. Each of these conveyance systems is susceptible to structural failure, blockages, and overflows. The U.S. Environmental Protection Agency (EPA) estimates that at least 23,000 to 75,000 sanitary sewer overflow events occur in the United States each year.

As new users are connected to centralized treatment, older conveyance and treatment systems must manage increasing flow or new treatment facilities must be constructed. It is estimated 532 new systems will need to be constructed by 2032 to meet future treatment needs.


Stormwater – runoff from rain or snow melt – also requires collection and treatment infrastructure. 39 states have one or more stormwater utility and seven states have 100 or more stormwater utilities. The number of communities with stormwater utilities or fees has grown from approximately 1,400 in 2013 to 1,600 in 2016.

In approximately 772 communities in the U.S., wastewater and stormwater drain into the same treatment system. These combined sewer systems can experience capacity issues following heavy rain events, resulting in overflows containing stormwater as well as untreated human and industrial waste, toxic substances, debris, and other pollutants. Called combined sewer overflows (CSOs), these occurrences can significantly impair water quality and impact public health and wildlife. After non-point source pollution (e.g., agricultural runoff and stormwater), combined sewer overflows are a leading source of water pollution in the U.S. The problem is exacerbated when communities have large amounts of impervious surfaces – concrete sidewalks, roads, parking lots, traditional roofs – that increase the amount of runoff entering the stormwater system.

Data on stormwater infrastructure and CSOs are limited. In 2016, the EPA released a report to Congress on CSOs in the Great Lakes region.  For the 184 CSO communities that discharge CSOs in the Great Lakes Basin, there were 1,482 CSO events in 2014, discharging an estimated 22 billion gallons of untreated wastewater into the Great Lakes Basin. Even these numbers were on the low side, as several communities did not report or have data available. In 2015, EPA finalized the National Pollutant Discharge Elimination System (NPDES) electronic reporting rule, requiring the filing of discharge monitoring reports; this will make more CSO data available to the public.