From Beachapedia

By Caroline Gleason
Last Updated: 7/27/21

Introduction to Cesspools

Cesspools are essentially lined pits in the ground that receive household sewage and wastewater, collect it and ultimately discharge it, untreated, back into the environment. They are substandard, outdated wastewater systems that have been banned from new construction in all 50 states and Puerto Rico.

Cesspools, along with septic systems, are a type of decentralized wastewater system used in areas without a centralized sewer system. An important distinction between these decentralized systems is that, unlike septic systems, cesspools are not designed to treat wastewater, only to dispose of it. Cesspools and septic systems may also be referred to as individual wastewater systems, on-site sewage treatment and disposal systems (OSTDS), or small community cluster systems.

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Figure 1. Cross Section of a Cesspool. Image courtesy of Michael Mezzacapo.

How do cesspools work?

Most cesspools consist of an underground concrete cylinder with an open bottom and/or perforated sides that provides a minimal barrier between the dug pit and the surrounding soils. Some cesspools are unlined, lacking that small separation between wastewater input and the environment.

Wastewater enters the cesspool through an inlet pipe. Once inside the system, gravity and density differences cause solids in the wastewater to separate; less dense matter like grease and oils float at the top while denser solids sink to the bottom. Naturally-occurring bacteria within the cesspool break down the settled solids through a process of anaerobic (without oxygen) decomposition. When cesspools are situated properly and functioning as best they can, the liquid wastewater, called effluent, leaches out of the lined pit into surrounding soil without any pretreatment. As the untreated effluent percolates through the soil, most of the pathogens (bacteria, viruses, etc) are filtered out or bind to dry soil particles. Eventually, the minimally-filtered effluent reaches the water table (the upper boundary of soil permanently saturated by groundwater) and flows into the groundwater.

While cesspools and septic systems are both household-scale, decentralized wastewater systems, it is important to note that septic systems (while not perfect) use a combination of technology and natural processes to treat household wastewater. Conventional septic systems usually consist of a buried, water-tight container called a septic tank, and a shallow, covered soil absorption field called a drain field. Organic matter in the wastewater breaks down in the septic tank, and that (partially) treated effluent is sent out to a drain field that is designed to have soil filter out harmful pathogens and contaminants before effluent flows into the groundwater. For any amount of disease-causing pathogens in the effluent to be successfully filtered by the soil, there must be at least two feet of dry, unsaturated soil for the effluent to percolate through before it reaches the water table, similar to septic systems. However, as basic holes in the ground, cesspools rarely have that two feet of soil to work with. [1] The system is designed to collect and concentrate wastewater in one location deep underground, which often means that cesspools are already at or below the depth of the water table, in direct contact with groundwater. Therefore, any pollution present in the wastewater entering the cesspool (including raw human sewage and disease-causing pathogens) can flow directly into the groundwater and contaminate drinking water wells, surface streams, and the ocean. That contamination goes on to cause harm to human health and the environment, including our beaches, marine life and coastal ecosystems such as coral reefs.

Current Use of Cesspools

Approximately 20% of households in the United States rely on a decentralized wastewater system, according to EPA. [2] This means approximately 1 in 5 US households rely on cesspools or septic systems for their wastewater management, and their use varies widely by region and state.

As of 2017, all 50 states and Puerto Rico have banned the permanent installation of new cesspools. Many states, like Hawai’i, are in the process of converting old cesspools into more effective wastewater treatment systems, whether that means transitioning to centralized sewer systems or to smaller-scale solutions, including technologies like advanced septic and package plants. States and municipalities have prioritized the upgrades of cesspools located close to surface waterways or the beach, which are more likely to put public health imminently at risk than cesspools located further inland.

That said, many cesspools are still in use around the country. States like New York and Rhode Island have legacy policies that allow existing cesspools to remain active. As of 2019, 75 percent of Suffolk County, NY (the easternmost of Long Island’s four counties) is unsewered, with approximately 360,000 residential onsite sewage disposal systems. [3] An estimated 250,000 of those systems are cesspools. [4] Hawai’i, the last state to ban cesspools, has approximately 88,000 active cesspools across the state (down from 90,000 just a few years ago). [5]

Alongside bans on the construction of new cesspools, many states have implemented tax incentives and financial aid programs to help homeowners with the cost of converting their cesspools to more advanced wastewater systems. Read more about these programs in the Policy Actions section later in this article.

Problems with Cesspools

How do cesspools fail?

Fundamentally, cesspools do not treat wastewater, only dispose of it. This is a failure by design.

As one example, cesspools in Hawai’i release approximately 53 million gallons of untreated sewage into the ground each day, according to the state’s Department of Health. [6] This wastewater contains harmful pathogens that can cause gastroenteritis, Hepatitis A, conjunctivitis, leptospirosis, salmonellosis and cholera, to name a few. [7] These discharges are not due to improper installation or infrequent maintenance; instead, this is a consequence of the system itself. With modern population growth and increased stress on our wastewater infrastructure, a wastewater system that does not treat sewage is dangerously outdated, and no longer a functional option.

How do cesspools pollute coastal waters?

The #1 water quality problem in areas serviced by decentralized wastewater systems like cesspools and septic systems is nitrogen contamination of fresh and marine waters. As described above, cesspools are basically lined pits in the ground that receive household wastewater. When cesspools are situated properly and functioning as best they can, the liquid effluent leaches out of the pit without any pretreatment and into the surrounding soil. While ideally the soil filters out most of the pathogens, the effluent that eventually reaches the groundwater is heavily polluted with nitrogen (and some phosphorus). The nitrogen-laden groundwater flows downstream towards surface waters like lakes, streams and, ultimately, the ocean. Cesspools-Graphic-Dry.jpeg Figure 2. Infographic: How do cesspools pollute in dry weather?

High concentrations of nitrogen in waterways have severe impacts on coastal ecosystems. Nitrogen acts as a fertilizer, causing algae populations to skyrocket in events called algal blooms. These increased populations of algae eventually die and sink to the bottom of the water body to decompose, which depletes the ‘’dissolved oxygen’’ in the water and often causes mass die-offs of fish, turtles, manatees and other aquatic life from the lack of oxygen and food sources. When this happens on a large scale, affected areas are called dead zones.

Drops in dissolved oxygen are not the only consequence of eutrophication, or the over-enrichment of nitrogen and other nutrients in waterways. In tropical regions, the algae cover reefs, starving corals of sunlight and oxygen. The subsequent, sudden loss of reef habitat has repercussions for fish, with one study finding 83% of the most abundant species either severely reduced or completely eliminated following an algal bloom in the Gulf of Oman. [8] In more temperate regions, high levels of nitrogen in the water lead to the decline of seagrass beds that provide nursery habitat for many important fisheries, as well as provide critical storage for atmospheric carbon as a blue carbon ecosystem. Eutrophication can also lead to an increase in harmful algal blooms and red tides that produce toxins that contaminate shellfish, cause fish kills and other sea life to die, and even threaten human health with a whole suite of mild to severe symptoms.

Cesspools-Graphic-Rain.jpeg Figure 3. Infographic: How do cesspools pollute in rainy weather?

Nitrogen pollution and its associated impacts are all happening during dry, “business as normal” conditions. The problems only get worse during wet weather, when rain and storm events cause local flooding which enables cesspools to discharge harmful, disease-causing pathogens into our recreational waters. Flood conditions saturate the soil with rainwater and runoff, which raises the water table so that there is little or no dry soil between the cesspool and groundwater to filter out pathogens (less than the two foot minimum requirement). These conditions allow cesspool effluent containing pathogens and nutrients to directly contaminate groundwater. If the runoff at the surface saturates the top layers of the soil, cesspool effluent can also leach into stormwater runoff to end up in surface waters even quicker. It is during these wet conditions that cesspools not only pollute coastal waters with nutrients that disrupt ecosystem balance, but also put human health at risk by discharging sewage pathogens into recreational waters.

How do cesspools pollute drinking water?

Many areas of the country that rely on shallow wastewater infrastructure like cesspools are also more likely to rely on groundwater for their drinking water supply. [9] For example, groundwater supplies approximately 95% of all domestic water in Hawai’i, a state with a high concentration of cesspools. [10] According to EPA, cesspool waters have often been found to have higher levels of nitrates and coliform bacteria (potential indicators of sewage pollution) than are allowed in drinking water. [11] Cesspools provide a direct pathway for harmful pathogens found in sewage to enter drinking water sources and make people sick.

Threats to Cesspools from Climate Change

Flooding from increasingly severe coastal storms associated with climate change will cause cesspools to pollute more frequently, releasing raw and under-treated sewage into coastal watersheds as surrounding soils become saturated during more frequent flood conditions. Furthermore, many coastal regions in the US are already experiencing recurrent flooding at high tide, in events aptly called high-tide flooding or sunny day flooding. Research shows that high-tide flooding events will become more common in areas already experiencing high-tide flooding, and will expand to currently unaffected areas as sea levels rise. [12]

In addition to more frequent flooding events, sea level rise also brings concerns of more direct groundwater contamination from cesspools and other shallow wastewater infrastructure, even away from the coast. Projected levels of sea level rise are set to raise water tables near the coasts which, in the case of cesspools, eliminates the minimal filtration of pathogens performed by dry soils. According to a study conducted across California, a coastal region with diverse topography and climate, 1 meter of sea-level rise is expected to expand the reach of areas flooded from below by approximately 50 to 130 meters inland, with low-lying coastal communities most at risk. [13] [14]

As mentioned above, many low-lying coastal communities in areas like New England, Long Island, and Hawai’i rely on both decentralized wastewater systems, and groundwater for their drinking water supplies. For cesspools, elevation of the water table associated with sea level rise means more contaminants, nutrients, and disease-causing pathogens will enter water sources that are also used for drinking water, for recreation and by wildlife. This exposure will risk harm to both human health and the environment.


Personal Actions

If you use a cesspool at home, the biggest action you can take is to convert it. Is your community considering moving towards a centralized sewer system or packaged plant? Is a smaller-scale solution like advanced septic a better option for you? There are many tax incentives and financial aid programs available to help alleviate the cost which are described in more detail below. Check with your state or local health department to see if there are any incentive programs in your area.

There are also actions we all can take to care for our wastewater systems, regardless of type. Good practices include:

  • Only flush the three P’s: pee, poop, and (toilet) paper.
  • Conserve water inside the house.
  • Don’t pour cooking grease or oils down the drain; instead, collect it in a container, freeze it, and throw it in the trash.
  • Try to avoid cleaners with petroleum additives or fillers, as they act like grease to cause blockages once they enter a wastewater system.
  • Skip the powder detergents for the same reason.

Alternative Technologies

Because cesspools do not perform any treatment of wastewater, there is no way to tinker with them to make them into an effective wastewater management system. They must be converted.

Where there is sewer infrastructure already in place or nearby, connecting homes and businesses that use cesspools to sewers and sewage treatment plants is the preferred option. A centralized wastewater system consists of a sewer system that transports wastewater to a central treatment plant. Sewer systems are either separated into stormwater sewers and sanitary sewers, or combined into a Combined Sewer Overflow that manages both stormwater and sanitary sewage or wastewater (although these are not recommended!). Wastewater that arrives at the central plant is treated before being discharged into the environment (or recycled). Many counties and municipalities have successfully made the switch from decentralized systems to centralized sewer over the years. Read more about one such success story from Monroe County in Florida, home of the Florida Keys, in the case study of our septic systems article

That said, centralized sewer systems are not always an easy, or even feasible, solution. Sewer systems can be costly to install in terms of money, time, and inconvenience - traffic disruptions not being an insignificant concern. Furthermore, for areas with unsuitable environmental conditions like shallow soils, impervious (unable for fluid to pass through) bedrock, or particularly vulnerable water tables, or even just where homes are too spread out, decentralized systems may make more sense. In those cases, cesspools can be converted to another, more effective decentralized option like a septic system.

Septic Systems, like cesspools, are on-site wastewater systems that usually consist of a buried, water-tight container called a septic tank, and a shallow, covered soil absorption field called a drain field. Conventional septic systems perform partial treatment of wastewater which, while an improvement on the zero treatment performed by cesspools, still does not help reduce nitrogen pollution in our waterways. New septic technologies are now available that are able to remove nearly 90% of the nitrogen in wastewater and have shallower drain fields that function better in coastal areas where the water table is usually pretty high. These advanced systems are more costly than conventional systems. Some states and local municipalities offer rebates and tax incentives to encourage homeowners to upgrade their wastewater systems, or require their installation for new construction.

Advanced treatment systems allow for additional treatment of wastewater beyond the limits of conventional septic, which helps reduce nitrogen pollution entering water sources. Individual systems are usually based around a septic tank, and therefore are often referred to as advanced septic technologies. There are two broad categories of advanced septic technologies: Aerobic or Advanced Treatment Units (ATUs) and Recirculating Media Filters (RMFs). Both categories use the addition of oxygen in the decomposition process to reduce nutrient loading and pathogens in the effluent before it is discharged to the drain field.

For areas better suited to a community-scale wastewater treatment system, package plants are modular systems that operate like miniature wastewater treatment plants. Package plants use a process called extended aeration to treat wastewater, which is a variation on the activated sludge process used by much larger plants. Standard package plants can produce high quality effluent that can be recycled as non-potable water for irrigation, aquaculture and industry applications.

Read more about these individual- and community-scale solutions in our article, Advanced Decentralized Wastewater Systems.

Policy Actions

As of 2017, all 50 states and Puerto Rico have banned permanent installation of new cesspools, and many states have efforts underway to convert remaining cesspools to more effective wastewater systems.

State governments have approached this process in a variety of ways: In Rhode Island, cesspools located within 200 feet of a water source (shoreline, public well, or water body used as a drinking water supply) must have been converted to another wastewater system by January 1, 2014. Cesspools not located near a water source are allowed to remain active through a legacy policy, but after January 1, 2016, must be converted within a year of the property changing ownership. [15] In New York, cesspools have been outlawed in new construction since 1973 but existing cesspools were allowed to be replaced with new cesspools up until July 1, 2019. Now, any cesspools in need of replacement must be upgraded to a different wastewater system that meets the standards set in the 1973 state law. [16]

In Hawai’i, legislation passed in 2017 requires the conversion of all cesspools in the state by 2050. The act directs the Hawai’i Department of Health to evaluate residential cesspools, develop a report that includes a prioritization method for cesspool upgrades, and work with the state’s Department of Taxation on funding options to help homeowners convert their systems. Read more about Hawai’i in the Case Study section later in this article. [17]

To help further defray the high cost of installing an advanced decentralized wastewater treatment system, many local county and town governments have implemented grant programs to urge homeowners to upgrade their systems. For example, Suffolk County, NY issued a mandate requiring the use of advanced septic in all new construction and renovations. [18] While not required, the county incentivized homeowners to choose to upgrade their current systems by offering up to $30,000 to eligible homeowners through their Septic Improvement Program Grant and Loan Program. On a federal scale, the Clean Water State Revolving Fund (SRF) also provides funding for upgrades to decentralized wastewater systems.

Case Study: Hawai'i

Cesspools are used throughout Hawai’i to dispose of sanitary waste, which has had serious consequences for human health and coastal environments around the Hawaiian islands. The estimated 88,000 cesspools across the state are estimated to discharge approximately 53 million gallons into the ground, and the groundwater, each day. [19] Groundwater provides approximately 95% of all domestic water in Hawai’i, according to EPA, which means that lots of Hawaiian residents are drinking and swimming and surfing in water likely contaminated by cesspools. [20]

EPA banned the use of large capacity cesspools (any cesspool serving 20 or more people) nationwide in 2005, and though the agency has forced the closure of over 3,600 of these large waste disposal pits since then, there remain nearly 1,400 in use as recently as 2020. [21] Even then, most of the cesspools in Hawai’i serve single-family residences and are therefore not subject to the 2005 EPA ban. [22] For many years, Surfrider Foundation's Hawaii Chapters worked with the state’s Department of Health to support changes to Hawaii's Administrative Rules to ban the installation of cesspools, including sending a 2014 letter of support for proposed rule changes banning the installation of new cesspools. Check out Surfrider’s campaign page for this effort here.

In 2016, Hawai’i became the last of the 50 states to ban the construction of new cesspools. [23] The following year, the state legislature passed a number of acts focused on phasing out cesspool use, including Act 125 which requires all cesspools statewide to be upgraded, converted, or closed by 2050. Act 125 also directed Hawai’i’s Department of Health (HDOH), the agency responsible for overseeing and permitting all onsite wastewater systems, to evaluate residential cesspools and develop a plan for how to prioritize cesspool upgrades. HDOH was instructed to work with the state’s Department of Taxation to provide tax incentives and financial assistance for homeowners to upgrade their cesspools, which included a temporary tax credit of up to $10,000 for each qualified cesspool to help cover the cost of upgrading or converting to a septic or aerobic treatment unit (ATU) system, or connecting to a central sewer system. The tax credit could be claimed between tax years 2016 to 2020. [24] The state also established a Cesspool Conversion Working Group to develop a long-range, comprehensive plan for converting all cesspools by the 2050 deadline. You can find the group’s published objectives here.

While progress has been made since this legislation passed, Hawai’i cesspools continue to release approximately 53 million gallons of untreated sewage each day. There is still a lot of work ahead. The state has so far prioritized the upgrades of cesspools nearest to water sources, which is defined as located within 500 feet of a shoreline, perennial stream, wetland, or within a source water assessment program, meaning it takes two years or less for wastewater to travel from a cesspool to a public drinking water source.[25] As mentioned earlier, groundwater provides 95% of Hawai’i’s water supply. [26] Reducing pollution coming from these high-priority cesspools can (and will) go a long way to protect public health and the environment statewide.

When it comes to what kinds of technologies to move towards, there are opportunities to implement new technologies for both centralized and decentralized wastewater systems. In areas suited to traditional sewer systems, wastewater treatment plants can (and should) implement wastewater recycling technologies to maximize reuse potential of treated wastewater. Read more about wastewater treatment and recycling in our **upcoming** Beachapedia articles on Sewer Systems and Wastewater Treatment.

However, extending central sewer systems out to serve more remote areas on the Hawaiian islands isn’t always feasible, and the process of building sewer lines and the treatment plants and pump stations to go with them can be both disruptive and prohibitively expensive for small, rural areas. For many, smaller-scale, decentralized wastewater systems may be the best solution, but it all depends on the local factors.

The cost of converting individual cesspools into another individual wastewater system can run in the tens of thousands of dollars, which could be a difficult thing to scale to the number of cesspools that must be converted statewide. Stuart Coleman, Surfrider’s former Hawai’i Regional Manager, proposes community-scale “distributed sewage management systems,” like package plants, which serve multiple households and prioritize recycling wastewater for reuse. [27] You can read more about these and other advanced decentralized treatment options here.

Additional Resources

Nature Conservancy “Where Does ‘It’ Go When I Flush?”
Hawai’i Department of Health’s Cesspools and Tax Incentives pages
EPA Cesspools in Hawai’i
TNC Reef Resilience Network’s Wastewater Pollution Toolkit
The Work to Convert Hawai’i’s Cesspools Continues
Video: How This Poo Problem Could Destroy the Hawaiian Islands


  1. Hawai’i Department of Health, Wastewater Branch. (2021, June). Cesspools
  2. US EPA. (2018, December). Septic Systems Overview
  3. Suffolk County Government. (2019, May 20). Suffolk Health Officials Outline Changes to Wastewater Practices to Take Effect On July 1, 2019.
  4. Suffolk County Government. (2019, May 20). Suffolk Health Officials Outline Changes to Wastewater Practices to Take Effect On July 1, 2019.
  5. Hawai’i Department of Health, Wastewater Branch. (2021, June). Cesspools
  6. Hawai’i Department of Health, Wastewater Branch. (2021, June). Cesspools
  7. Hawai’i Department of Health, Wastewater Branch. (2021, June). Cesspools
  8. Ella Davies. (2010, October 8). Toxic algae rapidly kills coral.
  9. US EPA. (2021, July). Large-Capacity Cesspools
  10. US EPA. (2021, June 7). Cesspools in Hawaii
  11. US EPA. (2021, July). Large-Capacity Cesspools
  12. Thompson, P. R., Widlansky, M. J., Hamlington, B. D., et al. (2021, June 21). Rapid increases and extreme months in projections of United States high-tide flooding.
  13. Befus, K. M., Barnard, P. L., Hoover, D. J., et al. (2020, August 17). Increasing threat of coastal groundwater hazards from sea-level rise in California.
  14. US Geological Survey. (2020, September 30). https://www.usgs.gov/center-news/new-model-shows-sea-level-rise-can-cause-increases-groundwater-levels-along-california-s?qt-news_science_products=1#qt-news_science_products New Model Shows Sea-level Rise Can Cause Increases in Groundwater Levels along California’s Coasts]
  15. Rhode Island Department of Environmental Management. (2015, September 1). Frequently Asked Questions: Rhode Island Cesspools Act
  16. Suffolk County Government. (2019, May 20). Suffolk Health Officials Outline Changes to Wastewater Practices to Take Effect On July 1, 2019.
  17. Hawai’i Department of Health, Wastewater Branch. (2021, June). Cesspools
  18. Suffolk County Government. (2019, May 20). Suffolk Health Officials Outline Changes to Wastewater Practices to Take Effect On July 1, 2019.
  19. Hawai’i Department of Health, Wastewater Branch. (2021, June). Cesspools
  20. US EPA. (2021, June 7). Cesspools in Hawaii
  21. Allan Parachini. (2020, June 22). Hawaii’s Cesspool Problem Continues to Bubble Up as EPA Cracks Down.
  22. US EPA. (2021, June 7). Cesspools in Hawaii
  23. Governor David Y. Ige. (2016, March 11). Hawaii Bans New Cesspools and Offers Upgrade Tax Credit.
  24. Hawai’i Department of Health, Wastewater Branch. (2021, June). Tax Credit Program and Qualifying Cesspools.
  25. Hawai’i Department of Health, Environmental Management Division. (2017, December). Report to the Twenty-Ninth Legislature... Relating to Cesspools and Prioritization for Replacement.
  26. US EPA. (2021, June 7). Cesspools in Hawaii
  27. Stuart Coleman. (2021, June 6). The Work to Convert Hawai’i’s Cesspools Continues.