Wastewater Infrastructure and Sewage Pollution

From Beachapedia

By Caroline Gleason
Last Updated: 7/27/21

Introduction to Wastewater Infrastructure and Sewage

Outdated wastewater infrastructure and poorly maintained or failing wastewater infrastructure threaten coastal water quality by discharging raw and under-treated sewage into local waterways and the ocean. Sewage can contain bacteria, viruses and parasites that make people sick with gastro-intestinal symptoms, rashes, flu-like symptoms, skin and eye infections and worse. Sewage discharges also pollute waterways with excess fertilizers that wreak havoc on coastal ecosystems by causing “nutrient loading” which fuels harmful algal blooms that put human health at risk, cause fish kills, threaten marine mammals and smother coral reefs.

An understanding of the basics of how the nation’s stormwater and wastewater infrastructure works is key in helping Surfrider’s activists and other concerned citizens who want to address sewage pollution problems that lead to beach closures, stressed coastal ecosystems, and harm to human health.

Types of Wastewater Infrastructure

In this article, we’ll introduce the five major types of wastewater infrastructure used in the US: cesspools, septic systems, separated sewer systems, combined sewer systems, and wastewater treatment plants. These infrastructure types can be broadly classified as either decentralized or centralized wastewater systems.

Decentralized Wastewater Systems

Decentralized wastewater systems, also called onsite wastewater systems, serve individual homes or small communities and are used in areas without a centralized [1] sewer system and wastewater treatment plant. This umbrella term includes cesspools and septic systems.

Approximately 20% of households in the United States rely on a decentralized wastewater system, according to EPA. [1] 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.


Cesspools are essentially lined pits in the ground that receive and collect household sewage and wastewater, then discharge it, untreated, back into the environment. [2] Most cesspools consist of an underground concrete cylinder with an open bottom and/or perforated sides. It provides a minimal barrier between the dug pit and the surrounding soils. Wastewater collects in the cesspool then leaches out of the lined pit to percolate through the surrounding soil without any pretreatment. Eventually, the minimally-filtered wastewater reaches the water table (the upper boundary of soil permanently saturated by groundwater) and flows into the groundwater.

Cesspools are substandard, outdated wastewater systems that have been banned from new construction in all 50 states and Puerto Rico. That said, many cesspools are still in use around the country. As of 2019, 75 percent of Suffolk County, NY (the easternmost of Long Island’s four counties) has approximately 360,000 residential onsite sewage disposal systems, an estimated 250,000 of which are cesspools. [3] 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). [4]

Read more in our Cesspools Beachapedia article.

Septic Systems

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. These systems use a combination of technology and natural processes to partially treat household wastewater from bathrooms, kitchen drains, and laundry. Wastewater flows from homes into the septic tank, which uses naturally-occurring bacteria and gravity settling as treatment. The liquid wastewater, called effluent, is then discharged to the drainfield where soils serve as a natural filter as the effluent flows downward toward the water table. For soil filtration to work, there needs to be at least two feet of dry, unsaturated soil under the drain field. When the depth of the drain field is too close to the water table, any nutrients or contaminants (including harmful, disease-causing pathogens) in the liquid effluent can directly pollute the groundwater, the surface waterways groundwater flows into and, eventually, the ocean.

In the US, more than 60 million people are serviced by septic systems, and approximately one-third of all new development in the US is serviced by septic or other decentralized treatment systems, according to EPA. [5] Septic use varies widely by region and state, with the highest concentration at 55% of households in Vermont and the lowest at 10% of households in California. [6] [7] When looking at absolute numbers, the state of Florida alone is responsible for over 12% of all septic systems in the US, according to the Florida Department of Health. [8]

Read more in our Septic Systems Beachapedia article.

Centralized Wastewater Systems

The majority of sewage infrastructure in the United States consists of centralized wastewater systems, in which sewage and wastewater from homes, businesses, medical facilities and more is discharged to a network of sewers, and transported to a central wastewater plant for varying levels of treatment. This is in contrast to the decentralized wastewater systems described above, which serve individual homes or small communities.

Sewer Systems

In most locations, there are two separate sewer systems -­ a stormwater sewer system and a sanitary sewer collection and treatment system. These systems have distinctly different purposes.

Stormwater sewers are gravity-driven systems designed to prevent flooding problems from rainwater runoff. [9] Civil engineers design these systems to be water superhighways; with the goal to get the rainwater and other urban runoff away from residential, commercial, and industrial areas as fast as possible to prevent flooding, and discharge it to a creek, river, or directly into the ocean.

Sewage collection and treatment systems, also sometimes referred to as sanitary sewer systems, collect and treat wastewater flowing from drains (toilets, sinks, showers, washing machines, and dishwashers) inside residences and businesses. Wastewater travels from households to treatment plants through a series of pipes called sewer lines. Like stormwater systems, sewer systems typically make maximum use of gravity to convey wastewater to a treatment facility. Because of this concept of gravity flow, treatment plants are frequently located in low areas next to rivers or the ocean. If wastewater does need to be pumped, the water flows into a concrete pit in the ground called a lift station or pump station, where pumps are used to transfer it through a force main (pressurized sewer) to the treatment plant. [10]

Read more in our Sewer Systems Beachapedia article.

Combined Sewer Overflows

Approximately 772 municipalities across the US use a third type of sewer system, called a combined sewer system, which is designed to collect rainwater runoff, domestic sewage, and industrial wastewater all in the same pipe for transport to a wastewater treatment plant. [11] In dry weather or during periods of light rain, combined systems are able to handle both stormwater and wastewater input and treat it before discharging it back into the environment. During periods of heavy rainfall or snowmelt, however, the wastewater volume in a combined sewer system often exceeds the capacity of the sewer system or treatment plant. When this happens, combined sewer systems are designed to overflow, discharging excess (untreated) wastewater directly to nearby streams, rivers, or other water bodies in events called combined sewer overflows (CSOs). Across the United States, CSOs release around 850 billion gallons of diluted yet raw sewage into surface waterways every year. [12]

Read more in our Combined Sewer Overflows (CSOs) Beachapedia article.

Wastewater Treatment Plants

Wastewater treatment, or sewage treatment, describes the biological, chemical and physical processes used to remove pollutants, nutrients, and suspended solids (including human waste) from the billions of gallons of wastewater produced every day, before the remaining water, called effluent, is returned to the environment or reused. [13] In the United States, these processes are most often performed at central wastewater treatment plants (sometimes abbreviated to WWTP). When sewage arrives at the treatment plant, it is typically treated using a combination of physical, chemical and biological treatment methods in stages referred to as primary, secondary, and tertiary treatment. Primary treatment consists of separation of liquids from solids, and secondary treatment utilizes special strains of aerobic bacteria (bacteria that need oxygen to grow) to break down the organic waste left after primary treatment. [14]

Wastewater may undergo tertiary treatment to become reclaimed water, which can be used for irrigation and other non-potable uses, or be treated even further to become recycled water that is good enough to drink. California’s Orange County Groundwater Replenishment System produces about 100 million gallons per day of high-quality, potable water that actually exceeds state and federal drinking water standards, and has greatly reduced the flow of partially treated wastewater into the ocean (more on this later). [15]

Read more in our Wastewater Treatment and Recycling Beachapedia article.

Causes of Sewage Pollution

Wastewater infrastructure in the United States has been neglected for years, decades even, which has resulted in a D+ grade from the American Society of Civil Engineers’ annual infrastructure report card. [16] Because of this neglect, sewage spills and infrastructure failures release approximately 900 billion gallons of under-treated sewage into surface waters every year, causing harm to public health and the environment. [17] It’s important to understand how sewage pollution gets to our waterways and beaches in order to best advocate for effective solutions moving forward.

Each type of infrastructure described in this article can fail as a method of wastewater treatment. Failures can happen in a number of ways, often as a consequence of poor maintenance or age. When these systems fail, they can pollute coastal waterways with poorly treated or untreated sewage, as well as excess nitrogen.

How Do Conventional Decentralized Systems Fail and Pollute Coastal Waters?

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

When it comes to conventional septic systems, failures are often a result of poor or infrequent maintenance. Homeowners with septic systems are expected to pay a company to pump their system every three to five years to clean out the solid sludge. When septic systems are not properly maintained, solids build up in the tank and cause overflows that could lead to untreated human sewage leaking into the drain field and maybe even nearby properties. [18] Septic systems also fail to treat wastewater if the septic tank is too close to (or at) the water table, which prevents the septic tank from effectively transporting effluent to the drain field, and instead allows nutrients and pathogens present in the wastewater to directly contaminate groundwater and the surface waterways it flows into. A submerged septic tank functions no more effectively than a cesspool, which is to say, not effectively at all. Too close of a proximity to the water table, or overSaturated soils can also cause back-ups in septic drainfields, driving effluent backwards towards the septic tank and causing overflows that leach sewage into homes, onto yards and into stormwater runoff that ultimately ends up in the ocean.

Even when septic systems are functioning at their best, and when there is enough dry soil to filter out most potentially harmful pathogens, the effluent that flows into the groundwater under the drainfield remains heavily polluted with nitrogen. This is also true of cesspools. Because of this, nitrogen pollution in fresh and marine waters is the #1 water quality problem in areas serviced by decentralized wastewater systems.

To read more about the consequences of nutrient pollution in our waterways, check out our Cesspools, Septic Systems, and Advanced Decentralized Systems articles here on Beachapedia.

How Do Centralized Wastewater Systems Fail and Pollute Coastal Waters?

Sewer systems can fail in a number of ways. Build-ups of fat and grease cause blockages in the system, which prevents the normal flow of wastewater to the treatment plant and can result in sewage backing up into streets, yards and even houses. Likewise, flushing foreign items like wipes and sanitary products (even wipes labeled “flushable”) can clog sewer lines and cause sewage backups. Tree roots can also grow into sewer lines, causing blockages similar to the grease build-ups described above. These obstructions can happen in main sewer lines, or in sewer laterals (also sometimes called “side sewers”), which are the underground pipes that connect residences or businesses to a main sewer line. [19]

When it comes to combined sewer systems, overflows are part of the system design. In order to avoid sewage from backing up onto the streets and into homes when it rains, combined systems were designed with bypasses that allow sewage and stormwater to flow untreated into nearby waterways, in discharges called Combined Sewer Overflows (CSOs). Over the last century, population growth and increased development in urban areas have contributed to greater flows of wastewater and stormwater that exceed the capacity of combined sewer systems and make CSOs more frequent and more problematic.

Over time, a very old, poorly maintained sewer pipe can simply corrode and crack. This allows rain and stormwater to infiltrate in and overwhelm the system’s capacity, causing overflows of un- or under-treated sewage into local waterways. [20] Cracked sewers lead to problems for treatment plants, which can only handle a certain volume of wastewater at any given time. When this capacity is surpassed, untreated sewage mixed with the stormwater that has seeped into the system will be released into local waterways to avoid backups in streets and homes, which can result in public health concerns and beach closures.

The primary concern with aging, neglected wastewater infrastructure is sewage spills, which are a major problem in the United States and will likely become more common due to climate change if we don’t invest in our wastewater infrastructure now. Human health impacts from sewage spills are a serious and growing concern; sewage pollution contains many harmful contaminants, including several types of disease-causing pathogens that can lead to symptoms like fever, diarrhea and vomiting, as well as even more dangerous diseases like typhoid fever and cholera. [21]

Read more about sewage spills and climate threats to centralized wastewater systems in our Sewer Systems, Combined Sewer Overflows (CSOs), and Wastewater Treatment and Recycling articles here on Beachapedia.


Just as each type of wastewater infrastructure described in this article can fail and pollute coastal waterways, each type also has specific actions and opportunities we can take to reduce sewage pollution.

Personal Actions We Can all Take

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

  • Only flush the three P’s: pee, poop, and (toilet) paper.
  • Throw other materials, including flushable wipes, in the trash (learn why here).
  • 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.
  • Check the ingredients and opt for natural personal care products (like soaps and sunscreen) when possible.
  • 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.

There are also specific actions you can take based on the type of wastewater infrastructure you use.

For those who have a cesspool or conventional septic system at home, consider upgrading to an advanced septic system, which allows for additional treatment of wastewater and helps reduce nitrogen pollution entering water sources by nearly 90%. 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. There are a number of local, state and federal policy initiatives to help cover the costs of upgrading to more advanced systems through grants, loans, and/or tax credits. Learn more about advanced septic and current incentive programs here.

If you have sewer infrastructure already in place or nearby, connecting homes and businesses on decentralized systems to sewers and sewage treatment plants is the preferred option, especially for areas with treatment plants that produce recycled water (more on this later). That said, centralized sewer systems are not always an easy, or even feasible, solution. Communities interested in collectively moving away from cesspools and conventional septic systems may consider something like a package plant, which is a modular, community-scale system that operates like a miniature wastewater treatment plant, treating up to 100,000 gallons of wastewater per day. Learn more about package plants here.

If you have a conventional septic system and upgrading to advanced septic is not an option, there are actions you can take to ensure your current system is functioning at its best:

  • Have your septic tank pumped every 3 to 5 years as recommended.
  • Space out your water use throughout the day to avoid flooding your septic tank.
  • Check for leaks in your faucets and toilets.
  • Use your garbage disposal sparingly.
  • Know where your septic tank is on your property, and keep an eye out for signs of failure.
  • Learn more here.

For those who are connected to a centralized sewer system, reducing stormwater and dry-weather urban runoff goes a long way to prevent sewer overflows in both separated and combined systems. Some ways to do this are:

  • Use as little water as possible.
  • Don't over-water your lawn, and adjust your sprinklers to avoid watering the pavement (it won't grow).
  • Consider installing an Ocean Friendly Garden to increase infiltration (rainwater that is *absorbed into the ground) and reduce runoff entering sewer systems.
  • Learn more about green stormwater infrastructure here.

Advocacy and Policy Actions

If you want to take action on a larger scale, you can advocate for wastewater recycling and reuse programs in your community. Water recycling simultaneously addresses a water supply problem, a waste disposal problem, and an ocean pollution problem, but many remain reluctant to fully embrace the opportunities wastewater recycling presents. Understanding and implementing water recycling requires a paradigm shift from thinking of “used” water as wastewater (something to get rid of as cheaply as possible) to thinking of it as the valuable, and limited, resource it is. Wastewater that has gone through primary and secondary treatment as well as further treatment by additional filtration and/or chlorination/dechlorination can be reused as reclaimed water (also sometimes called tertiary-treated water). It is often used for irrigation of parks, golf courses, and general landscaping. It is not potable, meaning it isn’t suitable for drinking.

Wastewater can also be treated to a higher standard than reclaimed water. A number of advanced treatment processes can be used to convert secondary or tertiary treated wastewater into water that is not only good enough to drink, but can exceed state and federal standards for drinking water. This is the case in Orange County, CA, where their Groundwater Replenishment System produces 100 million gallons of high-quality recycled water per day. Learn more about wastewater recycling here.

Significant investments are required to repair and replace our failing wastewater infrastructure, and government funding is available to pay for these necessary projects at the local, state and federal level. Many of the federal funding initiatives are managed by the US EPA, particularly through their Clean Water State Revolving Fund (CWSRF) which can be used for upgrading centralized sewer systems, wastewater treatment plants, and decentralized wastewater systems like those described here. [22]

Surfrider created our Stop Sewage Pollution campaign to help improve our wastewater infrastructure and ensure that all sewage in the US is adequately collected and treated to protect public and environmental health. This effort includes tracking state and federal policies, as well as operating the Blue Water Task Force, a national network of volunteers monitoring bacteria levels at more than 450 ocean, bay, estuary and freshwater sampling sites across the US.

Read more and get involved in our Stop Sewage Pollution campaign here.

Additional Resources

Beachapedia’s Wastewater Infrastructure Series

Septic Systems
Advanced Decentralized Wastewater Systems
Sewer Systems
Combined Sewer Overflows (CSOs)
Wastewater Treatment and Recycling

Mentioned in this Article

Blue-Green Algae and Cyanobacteria
Blue Water Task Force
Clean Water Act
Clean Water Initiative
Dead Zones
Green Infrastructure and Low-Impact Development
Harmful Algal Blooms
Health Threats from Polluted Coastal Waters
Ocean Friendly Gardens
Red Tides
Urban Runoff

Other Surfrider Resources

Stop Sewage Pollution Campaign
Clean Water Initiative
Clean Water Report (2020)
Surfrider’s “How does sewage pollution get to the beach?” series:


  1. US EPA. (2018, December). Septic Systems Overview
  2. Hawai’i Department of Health, Wastewater Branch. (2021, June). Cesspools
  3. Suffolk County Government. (2019, May 20). Suffolk Health Officials Outline Changes to Wastewater Practices to Take Effect On July 1, 2019.
  4. Hawai’i Department of Health, Wastewater Branch. (2021, June). Cesspools
  5. US EPA. (2018, December). Septic Systems Overview
  6. US EPA. (2018, December). Septic Systems Overview
  7. Kaye LaFond. (2015, October 16). Infographic: America’s Septic Systems
  8. Florida Department of Health. (2021, May). Onsite Sewage
  9. MSU Water. (2021). What’s the difference between Sanitary and Storm Sewers?
  10. Water Environment Federation. (2011, May). Access Water Knowledge: Sanitary Sewers
  11. US EPA. (2021, May 3). Combined Sewer Overflows (CSOs)
  12. US EPA. (2015, September 16). EPA Needs to Track Whether Its Major Municipal Settlements for Combined Sewer Overflows Benefit Water Quality.
  13. US Geological Survey. (2021). Wastewater Treatment Water Use
  14. US Geological Survey. (2021). Wastewater Treatment Water Use
  15. Orange County Water District. (2021). GWRS Frequently Asked Questions
  16. American Society of Civil Engineers. (2021). 2021 Report Card for America’s Infrastructure
  17. Surfrider Foundation. (2020). Clean Water Report
  18. Marlowe Starling. (2021). Out of sight, still a blight.
  19. US EPA. (2014, June). Private Sewer Laterals
  20. US EPA. (2021, July 10). Sanitary Sewer Overflows (SSOs)
  21. Everitt Rosen. (2021). Major spills from Florida’s sewage treatment plants are on the rise - and so are the storms that can cause aging pipes to burst.
  22. US EPA. (2021, July 3). Learn about the Clean Water State Revolving Fund (CWSRF)