Call Us Now: (415) 985-0155

How Does a Sewer System Work?

Oct 25, 2022 | San Francisco Plumbing

Do you often wonder what happens to all the sewage water and waste water from your home? Where does it all go? Well, that is what a sewer system is for. Sewer systems are complex networks of pipes and equipment that collect wastewater from homes and businesses and transport it to treatment facilities. They are typically owned and operated by municipalities. The sewer system is made up of several different components that work together to transport waste from your home to the treatment facility. These include collection pipes, pumps, lift stations, screens, flow meters, and other equipment.

One of the main functions of the sewer system is to collect wastewater from homes and businesses in your community. Wastewater consists of any liquid waste, such as water from the toilet, shower, or sink. The sewer system is also responsible for transporting this wastewater to treatment facilities, where it is treated and released back into the environment. This process helps to remove contaminants and reduce water pollution.

Components of a Sewer System

A sewer system is made of many components, all working together to carry out the functions and each of these components plays a different role.[1] They are collection pipes, pumps, lift stations, screens, and flow meters.

The Collection Pipe

The collection pipe is responsible for transporting wastewater from homes and businesses to treatment facilities. This can be done via gravity or using pumps that are powered by electricity. In some cases, a combination of both gravity and pumps can be used to transport wastewater.

Pumps and Lift Stations

Pumps and lft stations are used to move wastewater from lower elevations to higher points in the sewer network or treatment center. This is important because it allows water and sewage to flow through the system more easily.

Screens and Flow Meters

They are used to monitor the amount of water that is flowing through the system. These devices collect data on how much waste is being transported to sewage treatment facilities, which can help utilities identify potential problems in the system.

By carrying out their distinct function, each of these play an important role in helping cities and towns move wastewater efficiently through the system and to treatment facilities. Without these systems, sewage would accumulate in streets and buildings, creating health risks and environmental problems.

We offer high quality hydro jetting 

Sewer System: How the process works

Sewage water comes from a variety of sources within a community. It can include water from residential homes, businesses, and industrial facilities. This water contains human waste and other contaminants that must be transported to collection facilities for treatment before it can be released back into the environment.

Once collected, sewage water is typically transported through a series of pipelines to treatment facilities. These plants use various processes to remove contaminants and other impurities, including bacteria, viruses, chemicals, and heavy metals. The treated water can then be released back into the environment or used for other purposes such as irrigation or industrial processing.

The question now is how does sewage waste reach a processing plant? This varies depending on the location, as different areas often have different infrastructures and regulations in place. However, some common methods include gravity-fed pipelines that carry wastewater to treatment plants at higher elevations, pumping stations that help move wastewater through pipes with less elevation change, or a combination of both.

Sewage Water Treatment

Because sewage water is considered harmful to the environment, left untreated, they go through a series of intensive treatments before being released into the environment. These treatments go through a number of processes:

Primary treatment: 

During primary treatment, large solids in sewage water are removed by a process called screening. This process uses screens that remove objects such as rags, sticks, and other debris from the waste stream. [3]

Secondary treatment: 

The next step is secondary treatment, which involves using bacteria or other microorganisms to remove dissolved organic matter and some bacteria from the wastewater.

Tertiary treatment: 

If additional treatment is required, a process called tertiary treatment may be used. During this step, chemicals are added to the waste stream to break down remaining contaminants or microorganisms that cannot be removed by other means. This process involves several methods, which include:


This method involves getting rid of any remaining bacteria or microorganisms. This is usually done by  exposing the wastewater to ultraviolet light or chlorine gas.

Chemical treatment: 

In addition to disinfection, further chemicals may be added to the wastewater during this step. These include flocculants and coagulants, which bind with contaminants in water to form larger particles that can be removed by other treatment processes.

Types of Sewer Systems

Sewer systems come in different types [2] and each type has a These include combined sewers, sanitary sewers, and storm sewers.

Sanitary Sewer System

A sanitary sewer system is typically used to treat wastewater from homes and businesses. In these systems, the wastewater flows through underground pipes and is treated at a treatment plant before being released back into the environment.

Stormwater Sewer Systems

A stormwater sewer system is designed to carry rainwater runoff only. These systems are separate from sanitary sewers, and storm drains flow directly into streams, rivers, or lakes without going through any treatment process.

Combined Sewer System

A combined sewer is a system that carries both wastewater and stormwater runoff. In these systems, the wastewater from homes and businesses drains into one pipe, which then flows to a treatment plant. The storm sewers carry rainwater runoff directly to streams, lakes, or rivers without going through any treatment process. 

In most places in the United States, sanitary sewers and storm sewers are separate systems; water from sanitary sewers is treated at a wastewater treatment plant before being released back into the environment, while water from storm sewers is not. However, in some places, both sanitary sewers and storm sewers are combined into a single system. According to the United States Environmental Protection Agency (EPA), combined sewer systems were built in cities with growing populations where there was a need for large sewage treatment facilities.

In general, combined sewer systems collect all wastewater—from sanitary sources such as sinks, toilets, and showers—and stormwater runoff in the same pipe. During dry weather, wastewater flows to a sewage treatment plant for processing. During heavy rains or snowmelt, however, combined sewage systems discharge untreated sewage directly into a stream, river, lake, or bay. Because these systems are designed to handle the excess flow from storms, they are not equipped with the capacity to handle additional flows from melting snow and heavy rains. As a result, sewerage overflows occur when these systems become overwhelmed.

Common Sewer System Problems

Common sewer problems include:

  1. Sewer overflows
  2. Leaks and cracks in the sewer pipes
  3. Grease buildup and clogs in the system
  4. Corrosion or damage to sewer infrastructure
  5. Poor design or maintenance of the system

While there are a number of factors that can cause these common sewer issues, the most common cause is simply that the system becomes overwhelmed due to heavy rainfall or snowmelt. In fact, research has found that one of the main challenges facing modern cities is the need to upgrade aging sewer systems. These systems which are responsible for moving wastewater from homes and businesses to treatment facilities are often struggling to keep up with growing demands. In order to prevent these sewer issues and protect public health, it is important to invest in proper maintenance and upgrades to our aging sewer systems.

Some of the common causes of these sewer issues include

1. Grease buildup and clogs in the system

The buildup of grease and other debris can cause blockages that disrupt the flow of wastewater through the pipes. This can lead to overflowing manholes, backed-up toilets, and other problems.

2. Broken or leaking sewer pipes

Over time, pipes can become damaged or corroded due to exposure to the elements or shifting ground. Leaks can allow wastewater to seep out of the system and cause flooding in streets and other public areas.

3. Excessive tree roots in the sewer system 

Trees can cause problems in your sewer pipes as well. Tree roots can grow into and expand cracks in the pipes, causing blockages or leaks that disrupt wastewater flow.

4. Aging infrastructure

Some of the infrastructures in the United States are aging pretty fast and as such are also experiencing a variety of problems due to poor maintenance, climate change, and other factors. Over the past 100 years, much of our sewer infrastructure has failed to keep up with growth and development. As a result, many areas are experiencing reduced flow rates or rising utility bills as utilities struggle to maintain their systems in a state of good repair.

5. Stormwater infiltration

When it rains and storms, stormwater can infiltrate and enter sewer lines through manholes or cracks in the pavement, causing a problem known as infiltration. This can happen when there is an insufficient or faulty infrastructure to prevent it. The result is untreated wastewater flowing into local waterways, which can lead to pollution and health hazards if left unattended. One of the biggest challenges facing our nation’s sewer systems today is stormwater infiltration. This occurs when rain or other precipitation enters the sewer lines through cracks in the pavement or manholes, causing an increase in untreated wastewater flowing into local waterways and potentially leading to pollution and health hazards. [4]

Sewer System Maintenance

Sewer systems are a crucial part of modern life, but they can also present serious hazards if they are not properly maintained. Keys to maintaining the sewer system include:

  1. Regular inspections and cleaning of sewers and drains to remove dirt, debris, and blockages.
  2. Use of backflow prevention devices to reduce the risk of wastewater overflows in the event of a break or failure in the system.
  3. Getting adequate funding and resources for ongoing maintenance and repairs.
  4. Another important step is to treat wastewater before it enters the sewer system in order to reduce the risk of contamination or disease outbreaks.

While sewer systems are typically managed by city or county governments and it would seem that they are responsible for the care and maintenance of sewer systems, individuals can also take steps to help maintain their own sewers and septic systems. These steps can go a long way to preserve the lifespan of sewer systems:

  1. Installing filters in drains and toilets to prevent debris from entering the system.
  2. Performing routine maintenance checks and repairs.
  3. Using water efficiently to reduce strain on the sewer system
  4. Working with city officials and community members to identify and address issues that arise in the sewer system.

Maintaining a sewer or septic system is an important part of helping to keep our communities safe, healthy, and sustainable. By taking steps like installing filters, performing regular maintenance checks, using water efficiently, and working together with city officials and community members, we can all do our part to keep the sewer system running smoothly.

But when you sewer system needs repair, contact O’Grady Plumbing without hesitation.



  1. How Sewer and Septic Systems Work. How Stuff Works.    
  2. How Do Sewer Systems Work? Interesting Engineering Inc.  
  3. How Septic Systems Work. United States Environmental Protection Agency.     
  4. How Does Sewage Treatment Work? Scientific American.   


Read More

Related Posts

We’re On It!

Emergency Services Available – 30 Minute Response Time.