Storm Sewer vs Sanitary Sewer

With the ongoing of the building of towns and cities the people that built these societies realized that in order to control populated areas from flooding separating stormwater from sewage made practical sense and management in urban development. What’s the Difference between Sanitary Sewers and Storm Sewers? Storm Sewer VS Sanitary Sewer

Sanitary Sewers carry sewage from bathrooms, sinks, and kitchens. Before being released to rivers & creeks it’s treated according to EPA standards.
Storm Sewers are designed to carry rainwater or melting snow through an underground system that ends up in nearby rivers, creeks to prevent flooding.

Most runoff is conveyed directly to nearby streams, rivers, or other water bodies (surface water) without treatment. As the city gets older the two systems along with other Infrastructure become unmanagable and in disrepair.

Storm Water Management


 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.

This water can contain harmful pollutants from motor oils to road salt that can have a huge effect on neighboring streams.

Engineered storm water design and “green infrastructure” can capture and reuse storm water to maintain or restore natural hydrology’s and give the storm water more time by using some creative design whenever development is studied and proposed. It is up to the managers that 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 the Drains on corners of streets that become clogged. Large Storm Lines can be monitored and televised the replaced in sections with good planning. Relining broken or cracked lines. sealing or replacing manholes on Sanitary Sewers can stop a lot of Infiltration problems from groundwater.

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. An NPDES permit  (National Pollutant Discharge Elimination System) is typically a license for a facility to discharge a specified amount of a pollutant into receiving water under certain conditions.

  Detaining storm water and removing pollutants is the primary purpose of storm water management. Pervious Surfaces that are porous and allow rainfall and snowmelt to soak into the soil, Gray infrastructure, such as culverts, gutters, storm sewers, conventional piped drainage, and Blue/Green infrastructure that protect, restore, or mimic the natural water cycle, all play a part in storm water 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 water shortage, there is a new design that is sensitive to Storm Water Management.

This new methodology treats water more like a natural resource that can solve water problems by building natural solutions into the planning and functioning of the city as it’s being built or added afterward.

In the past building, a city would cause an environmental impact on surrounding areas of the community. This new way of thinking harnesses the potential that water can contribute and uses them in the design of the city.

In a Water Sensitive Design city, natural green space and vegetation are retained in strategic areas that are developed inside the city. These green spaces along with soil help with the natural filtering process and hydraulic control that would be found outside where the hard surfaces of the city don’t exist.

What Are Sanitary Sewers and Why Are They Important

Sanitary Sewers collect and transport domestic, commercial, and industrial wastewater and typically only limited amounts of stormwater and infiltrated groundwater gets through the manholes and sewer lines to treatment Wastewater plants and facilities for treatment. Storm Drains and Sanitary Systems are normally independent of each other.

You cannot always tell the difference by looking at them. Generally, storm drains are outside and sewer drains inside but not always. Sanitary sewer system collects water from inside our homes and businesses and carries it to a treatment plant where the wastewater is cleaned before being released into rivers and streams.

Treatment plants are engineered to process a certain population and strength of sewerage and 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 snowball effect on the whole system.

Much of the same maintenance programs that are used on 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.

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 can solve a lot of the problems faced by older towns and cities that built their infrastructure right after World War 11 or before.

Wastewater Plants are designed to treat a certain amount of flow.  Process control is based on being able to control surges of Stormwater coming into the plant. As with older systems rain storms double or even triple the amount of flow coming into the Wastewater plant which ends up inundating the plant causing environmental spills and even fish kills.

Most small towns and cities can’t keep up with the enormous money and task of repairing older infrastructure. This is happening across America where aging pipes and Pump Stations are deteriorating with a lack of enough funds to replace existing infrastructure.

In the coming years especially with the emerging problem of Water Scarcity, more creative ways of dealing with these issues are going to press cities and towns relinquish their responsibilities and hand over the keys to Private Companies which is already happening or Regionalization.

What is a Combined Sewer

Combined sewer system (CSS) collects rainwater runoff, domestic sewage, and industrial wastewater into one pipe. Under normal conditions, it transports all of the wastewater it collects to a sewage treatment plant for treatment, then discharges to a water body.

The volume of wastewater can sometimes exceed the capacity of the CSS or treatment plant (e.g., during heavy rainfall events or snowmelt). When this occurs, untreated stormwater and wastewater discharge directly to nearby streams, rivers, and other water bodies.

Combined sewer overflows (CSOs) contain untreated or partially treated human and industrial waste, toxic materials, and debris as well as stormwater. according to EPA

Sanitary Sewer Overflows (SSO)

There are times that Sanitary Sewers will release sewerage because of operational problems. These releases are called Sanitary Sewer Overflows or (SSOs) SSOs can contaminate local rivers and streams, causing serious water quality problems, and back-up into homes, causing property damage and threatening public health.

Possible Problems that can cause SSOs can include:

  • blockages,
  • line breaks,
  • sewer defects that allow stormwater and groundwater to overload the system,
  • power failures,
  • improper sewer design, and
  • vandalism.

EPA estimates that there are up to 750,000 SSOs reported every year not including the sewage backups in buildings and homes like the Roto-Rotor kind that happens every day.

These kinds of problems are normally investigated and are looked at seriously by  EPA according to NPDES permits that are held by the municipalities or governments that can result in fines or action against the permit holders.

Having worked in the Water/Sewer Utility Grid since the 70’s I’ve seen the old and the new and now it’s the crumbling infrastructure that has been coming for some time now.

The Basics of Development are Storm Water and Sanitary Sewer Systems. Pollution from these two deteriorated systems is unseen but very real.

The new approaches using Stormwater in Green Urban Design are exciting and the new technologies in Wastewater reuse is not a dream, it’s a reality that some cities are using and should be implemented now!

What’s the alternative? Can we squeeze another couple of decades out of an ancient infrastructure for our kids to worry about it?

Jim has worked in Water/Wastewater and Water Filtration Business as a Consulting Operator for over 30 years and has written more than 300 articles on the Worldwide Water Situation.


Author/Editor, MyWaterEarth&Sky

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