Storm Sewer vs Sanitary Sewer: Understanding the Differences

In order for the proper planning and development of a community with the public’s health and protection of the environment as a goal. There are two underground systems at work to ensure the city operates. What is the difference between a Storm Water System and a Sanitary Sewer System?

Storm Water System:

  • Collects outside runoff rain & snowmelt
  • Transports it to waterways preventing flooding-Under NPDES Permit

Sanitary Sewer System:

  • Collects & transports for treatment of domestic, commercial & industrial wastewater from inside buildings
  • Normally Separate from the Storm SystemUnder NPDES Permit

When American cities and towns were developed infrastructure was put in place to last for 100 years or so. Each system is able to work in conjunction performing a necessary function that was genius in its time.


In any community, ensuring effective water disposal is key. Central to this are two systems: storm sewers and sanitary sewers. Yet, many folks are unclear about their distinct roles and functionalities. This article looks into these two integral components of urban living – storm sewer vs sanitary sewer – underlining the differences and the importance of each one. Through MyWaterEarth&Sky expertise, we aim to foster a deeper understanding of the pivotal yet often overlooked elements of our neighborhoods and cities and literally what is right under our feet.


Storm Sewer vs Sanitary Sewer: Understanding the Difference


When we talk about sewer systems, most people think of sanitary sewers which are designed to carry sewage from households and other buildings. However, another important yet often overlooked part of our urban infrastructure is the storm sewer, a system designed to carry rainfall runoff and other drainage but not sewage. While both sanitary and storm sewers play crucial roles in our cities, understanding the differences between the two is essential.

The storm sewer is designed to address storm-related issues. During heavy rains, this system drains off excess water from streets and other paved areas. The storm sewer carries away rainwater, melted snow, and other storm-generated runoff. By doing so, the storm sewer helps prevent flooding, water damage, and the subsequent spread of diseases.

Sanitary Sewers, on the other hand, sanitary sewers are underground pipes that transport sewage from houses, businesses, and other buildings to treatment facilities. Unlike the storm sewer, the sanitary sewer carries wastewater from sinks, toilets, and other plumbing facilities, treating it before it is discharged back into the environment.

Both storm and sanitary sewers are crucial elements of our communities. They perform different yet complementary roles in managing water and sewage, helping to keep our cities clean and our environments safe.

The main difference between a storm sewer and a sanitary sewer lies in their unique functions: one drains rainwater and runoff, and the other carries away our daily sewage. Understanding these differences helps us appreciate the complexity and importance of our sewer systems.


Understanding Storm Water Collection and Sewer Systems


In order to understand the contrast between sanitary and storm sewer systems, it’s key to understand what each one does. The storm drain system is designed to quickly carry rainwater or runoff away from your home. This spotlights the primary role of storm sewers; they are designed to prevent flooding and transport rainwater that falls in urban areas.

During a heavy storm, water runs along the streets into storm drains. Part of the city’s overall water collection system, these storm drains serve as gateways to the storm sewers, allowing rainwater to flow unobstructed, reducing the risk of urban flooding. So don’t confuse stormwater with wastewater; these storm drains take care only of rainwater.

On the other hand, sanitary sewer systems carry sewage from homes and buildings via underground pipes to a wastewater treatment plant. This water, chiefly from kitchens, bathrooms, and laundries, is then treated and released back into the environment. The city’s sanitary sewer collection system consists of pump stations, pipelines, manholes, and other infrastructure working together to transport wastewater efficiently and safely.

Compared to the storm sewer system, the goals are different but equally important. One tackles the vast volumes of stormwater, reducing flood risks, while the other safely transports wastewater away from home, safeguarding public health and the environment. Understanding these differences can help homeowners make informed decisions while dealing with water issues at home.

Storm Drains collect runoff from your local area and transport it to local streams, lakes, and wetlands keeping your town or city protected from flooding.

They also help remove the trash, litter, and other undesirable waste that ends up in areas of rivers and streams. This can help protect your city’s waterways. It’s a layer of added protection because once trash and litter from the street get into the environment it’s harder to deal with.

The Storm Drain is not made for chemicals or pollutants that can be detrimental to the environment and waterways. Oil and other fluids from cars end up in the Storm Drain but aren’t intended to. Litter and trash that end up on the ground will eventually end up in the water and moved to a waterway or stuck in the grates to be manually removed by city workers.


Where Does Storm Water Go?


Key Differences Between Storm Sewer and Sanitary Sewer Systems


The Storm Sewer and Sanitary Sewer Systems play vital roles in the management of water and waste in urban areas. The storm sewer, unlike the sanitary sewer, is designed to handle surface runoff from rain, melting snow and ice, and other weather events. As a part of the larger sewer system, storm sewers help prevent flooding and water damage by directing excess water away from structures and pushing the excess water into nearby waterways keeping traffic moving and streets dry.

Sanitary Sewers, on the other hand, are designed to transport sewage from residential, commercial, and industrial facilities to a wastewater treatment plant. Unlike the storm sewer, which handles runoff, the sanitary sewer is specifically intended for contaminated waste and is an integral part of the sewer system.

The lines or manholes are covered or replaced to avoid rainwater or snowmelt from the ground. Controlling the amount of water that is being moved in the collection system. Keeping this sewer line in good shape is critical to prevent problems such as sewer backup or the need for sewer repair.

The differences between the storm sewer and sanitary sewer are also apparent during times of heavy rainfall. The storm sewer will convey the increased volume of water to nearby ponds, streams, or rivers, while the sanitary sewer will continue to transport sewage to a treatment facility.

Both contribute significantly to the overall health and efficiency of the sewer system. Some cities need NPDES permits before they can discharge stormwater to area waterways that have to be monitored and reported to State and Federal Agencies.  Detaining stormwater and removing pollutants is the primary purpose of stormwater management.

Water Sensitive Urban Design is becoming very popular in new developments and Infrastructure repair. It’s a newer approach to the old thinking of dealing with changing environments. With new ongoing problems involving water scarcity and water shortage, there is a new design that is sensitive to Storm Water Management.

Understanding the key differences between storm sewer and sanitary sewer systems is vital when it comes to maintenance or sewer repair. While they both form parts of the complex sewer system, they have different purposes and handle different types of waste. Knowing this can help in implementing proper operation and maintenance routines, resulting in a more efficient and reliable sewer system.

How Does a Sanitary Sewer Work?

Effective Sewer Repair for Both Storm and Sanitary Sewer Systems


Both storm and sanitary sewer systems play a significant role in our water cycle. Each system needs effective sewer repair to keep both operating properly. Both sewer systems are essential for managing wastewater and maintaining the health of the environment and efficient operation of the city.  However, distinguishing between storm, sanitary sewer, and sewer drains can be an ongoing task.

Typically, a storm sewer is designed to carry rainwater away during a storm. They directly collect the water and route it to area waterways. This system is vital during a storm and aims to prevent flooding and water-logged areas. On the other hand, a sanitary sewer, designed differently, manages wastewater from our domestic and industrial activities. This sewage needs to go through a treatment process before it is released to those area waterways.

In urban and developed areas, blacktop pavement and roofs are considered impervious surfaces that prevent rain and snow melt-off from naturally soaking into the ground. Instead, water runs rapidly into storm drains, sewer systems, and drainage ditches and can cause flooding, erosion, turbidity, storm, and infiltration into the Sewer System, along with infrastructure damage.

It is up to the city and town managers who are in charge to come up with these planning ideas. Storm Water Systems and Storm Drains can be maintained and improved by a simple cleaning of the Drains on corners of streets that become clogged.

Treatment plants are engineered to process a certain population and strength of sewerage but can’t accept the large amounts of Storm Water that can come from area flooding and snowmelt. Infiltration and inflow (I/I)  through old sewer pipes can have a huge effect on the whole system creating pollution in waterways connected to storm drains.

Much of the same maintenance programs that are used in Storm Water Management are used to improve Sanitary Sewer Systems. Collection pipes are repaired and or replaced by televising the lines and locating problem areas or sections.

Irrespective of the sewer system, a City needs a team that is equipped to provide prompt and efficient repair services. A dysfunctional sanitary sewer could lead to water pollution. They both need to prioritize regular monitoring and maintenance to prevent such occurrences.

At MyWaterEarth&Sky we are dedicated to providing water solutions that resonate with respect and care for our natural resources. Our work in sewer systems and water reclamation demonstrates our commitment to sustainable practices. Trust us to service and maintain your storm and sanitary sewers, ensuring the safe flow of wastewater and stormwater. In the face of a storm, our technicians are ready and capable of wrestling the storm to ensure you’re not left battling water-related issues.



In conclusion, understanding the difference between a storm sewer and a sanitary sewer is essential for proper sewage management. Both systems play vital roles in a community. The storm sewer dispels excess rainwater and prevents flooding, while the sanitary sewer treats wastewater before it is discharged back into the environment. Adequate knowledge of the two systems promotes better waste disposal practices and environmental sustainability. At MyWaterEarth&Sky we are committed to educating the public on these vital infrastructures for an improved and more sustainable future.



JimGalloway Author/Editor



What Is Stormwater Management and Why Is It Important?

EPA-National Pollutant Discharge Elimination System (NPDES) 


Q: What are the primary functions of storm and sanitary sewers?
A: The primary function of storm sewers is to drain off excess water from streets and other paved areas during heavy rains, thereby preventing flooding and water damage. On the other hand, sanitary sewers carry sewage from households and other buildings to treatment facilities where it’s treated before discharge.
Q: How do storm and sanitary sewers help in maintaining environmental safety?
A: Both storm and sanitary sewers play crucial roles in maintaining environmental safety. The storm sewer system prevents flooding and water damage, while the sanitary sewer system treats wastewater from buildings before reintegrating it into the environment, helping to keep our cities clean and safe.
Q: What is the key difference between storm sewers and sanitary sewers?
A: The key difference lies in their unique functions. The storm sewer drains rainwater and runoff, and the sanitary sewer carries away daily sewage. They play different yet complementary roles in managing water and sewage.
Q: What roles do storm and sanitary sewer systems play in urban areas?
A: The storm sewer system carries away excess water during weather events like heavy rains, helping prevent flooding and water damage. The sanitary sewer system, on the other hand, transports sewage from residential, commercial, and industrial facilities to a wastewater treatment plant for treatment and release back into the environment.



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