EPA, in partnership with states, territories and the District of Columbia, conducts the CWNS every four years. Congress requires EPA to conduct the CWNS under sections 205(a) and 516 of the Clean Water Act (CWA) (33 U.S Code §1375).

The CWNS is a comprehensive assessment of the capital costs (or needs) to meet the water quality goals of the CWA and address water quality and water quality related public health concerns. Every four years, the states and EPA collect information about:

• Publicly owned wastewater collection and treatment facilities
• Stormwater and combined sewer overflows control facilities
• Nonpoint source pollution control projects
• Decentralized wastewater management

EPA collects information about these facilities and projects including: 

• Estimated needs to address water quality or water quality related public health problems.
• Location and contact information for facilities and projects.
• Facility populations served, flow, effluent, and unit process information.
• Nonpoint source pollution control best management practices.

EPA documents national and state needs in a Report to Congress used by Congress and state legislatures in their budgeting efforts. The data are also used to: 

• Help measure environmental progress.
• Contribute to academic research.
• Provide information to the public.
• Help local and state governments implement water quality programs.

CWNS Capital Investment Needs

CWNS data on capital investment needs are organized into the following categories:

• I. Secondary Wastewater Treatment

  This category includes needs and costs necessary to meet the minimum level of treatment that must be maintained by all treatment facilities, except those facilities granted waivers of secondary treatment for marine discharges under section 301(h) of the Clean Water Act. Secondary treatment typically requires a treatment level that produces an effluent quality of 30 mg/l of both BOD5 and total suspended solids (secondary treatment levels required for some lagoon systems may be less stringent). In addition, the secondary treatment must remove 85 percent of BOD5 and total suspended solids from the influent wastewater.

• II. Advanced Wastewater Treatment

  This category includes needs and costs necessary to attain a level of treatment that is more stringent than secondary treatment or produce a significant reduction in nonconventional or toxic pollutants present in the wastewater treated by a facility. A facility is considered to have Advanced Wastewater Treatment if its permit includes one or more of the following: Biochemical Oxygen Demand (BOD) less than 20mg/l; Nitrogen Removal; Phosphorous Removal; Ammonia Removal; Metal Removal; Synthetic Organic Removal.

• III-A. Infiltration / Inflow (II) Correction

  This category includes needs and costs for correction of sewer system infiltration/inflow problems. Infiltration includes controlling the penetration of water into a sanitary or combined sewer system from the ground through defective pipes or manholes. Inflow includes controlling the penetration of water into the system from drains, storm sewers, and other improper entries. It also includes costs for preliminary sewer system analysis and detailed sewer system evaluation surveys.

• III-B. Sewer Replacement / Rehabilitation

  This category includes needs and costs for the maintenance, reinforcement, or reconstruction of structurally deteriorating sanitary or combined sewers. The corrective actions must be necessary to maintain the structural integrity of the system.

• IV-A. New Collector Sewers and Appurtenances

  This category includes the needs and costs of new pipes used to collect and carry wastewater from a sanitary or industrial wastewater source to an interceptor sewer that will convey the wastewater to a treatment facility.

• IV-B. New Interceptor Sewers and Appurtenances

  This category includes needs and costs for constructing new interceptor sewers and pumping stations to convey wastewater from collection sewer systems to a treatment facility or to another interceptor sewer. This category includes needs and costs for relief sewers.

• V-A. Combined Sewer Overflow (CSO) Correction – Traditional Infrastructure

  This category includes needs and costs to prevent or control the periodic discharges of mixed stormwater and untreated wastewater (CSOs) that occur when the capacity of a sewer system is exceeded during a wet weather event. This category includes traditional CSO control infrastructure such as collection, storage and treatment technologies. This category does not include needs and costs for overflow control allocated to flood control, drainage improvement, or the treatment or control of stormwater in separate storm systems.

• V-B. Combined Sewer Overflow (CSO) Correction –Traditional Infrastructure

  This category includes needs and costs to prevent or control the periodic discharges of mixed stormwater and untreated wastewater (CSOs) that occur when the capacity of a sewer system is exceeded during a wet weather event. This category includes green infrastructure CSO control infrastructure such as upland runoff control techniques. This category does not include needs and costs for overflow control allocated to flood control, drainage improvement, or the treatment or control of stormwater in separate storm systems.

• VI. Stormwater Management Program (pre-2008 needs only)

  This category includes the needs and costs to plan and implement structural and nonstructural measures to control the runoff water resulting from precipitation (stormwater). It includes controlling stormwater pollution from diffuse sources by (1) reducing pollutants from runoff from commercial and residential areas that are served by the storm sewer, (2) detecting and removing illicit discharges and improper disposal into storm sewers, (3) monitoring pollutants in runoff from industrial facilities that flow into municipal separate storm sewer systems, and (4) reducing pollutants in construction site runoff discharged to municipal separate storm sewers.

  Needs and costs may be reported for Phase I, Phase II, and non-traditional (e.g., universities, prisons, school districts) municipal separate storm sewer systems (MS4). Unregulated communities can also report needs and costs in this category (formerly reported in VII-D: NPS-Urban).

  Only pre-2008 needs and costs are in Category VI. Beginning in the 2008 survey and continuing for future surveys, Stormwater Management Program needs and costs must be reported in sub-categories A-D described below.

• VI-A. Stormwater Conveyance Infrastructure

  This category includes the needs and costs to address the Stormwater Management Program activities associated with the planning, design, and construction of conveying stormwater via pipes, inlets, road side ditches, and other similar mechanisms.

• VI-B. Stormwater Treatment Systems

  This category includes the needs and costs to address the Stormwater Management Program activities associated with the planning, design, and construction of treating stormwater with wet ponds, dry ponds, manufactured devices, and other similar means.

• VI-C. Green Infrastructure

  This category includes the needs and costs to address the Stormwater Management Program activities associated with the planning, design, and construction of low impact development and green infrastructure, such as bioretention, constructed wetlands, permeable pavement, rain gardens, green roofs, cisterns, rain barrels, vegetated swales, restoration of riparian buffers and flood plains, etc. Projects in this category can be both publicly-owned and privately-owned.

• VI-D. General Stormwater Management

  This category includes the needs and costs to address the Stormwater Management Program activities associated with implementing a stormwater management program, such as Geographic Information Systems (GIS) and tracking systems, equipment (e.g., street sweepers, vacuum trucks, etc.), stormwater education program start-up costs (e.g., setting up a stormwater public education center, building a traveling stormwater education display), and stormwater management plan development.

• X. Recycled Water Distribution

  This category includes the needs and costs associated with conveyance of treated wastewater that is being reused (recycled water), including associated rehabilitation/replacement needs. Examples are pipes to convey treated water from the wastewater facility to the drinking water distribution system or the drinking water treatment facility and equipment for application of effluent on publicly-owned land.

  The needs and costs associated with additional unit processes to increase the level of treatment to potable or less than potable but greater than that normally associated with surface discharge needs are reported in Category II.