What can be done to reduce inflow and infiltration?

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A diagram of two pipes, one showing sources of inflow and the other showing sources of infiltration.

The sanitary sewer system accommodates a range of wastewater volumes, but there are limits. Inflow and infiltration (I&I) is clear water—from storm drainage and groundwater—that enters sanitary sewer pipes. Once in the system, it becomes wastewater and adds volume to the water to be treated by the regional plant.

Clear water from I&I puts unnecessary stress and costs on local and regional systems, while decreasing available capacity.

Consequences of I&I

I&I pushes wastewater treatment to
the maximum and can result in:

  • Upgrades to existing systems to
    accommodate larger volumes
    of water
  • Sewer backups or overflows
  • Environmental impacts
  • Maintenance repair costs

Sources of I&I

I&I enters the wastewater systems
as clear water via:

  • Open maintenance holes
  • Defective sewer laterals
  • Improper sump pump connections
  • Gutters directing water to sewers
  • Uncapped sewer lateral cleanouts
  • Aged or broken municipal sewer pipes

Reducing I&I

Ways to help keep clear water
and wastewater separate:

  • Examine stormwater connections
  • Inspect sewer laterals
  • Cap sewer lateral cleanouts
  • Repair sewer laterals
  • Check sump pump discharge points
A diagram showing a cross-section of a pipe containing sanitary flow and clear water from inflow and infiltration, before and after remediation and reduction of I&I.

Inflow and infiltration (I&I) reduction

When clear water enters the sewer system through inflow and infiltration (I&I), it is treated unnecessarily. Inspect sewer laterals, sump pumps and gutters to help save local resources and prevent issues on your property like contamination, sinkholes or serious damage.

Inspect and maintain laterals

Blockages, cracks, holes and root infiltration in private sewer laterals can prevent the flow of sewage and allow groundwater to seep in. Work with a local plumber or video inspection service to understand the state of your lateral. Then plan for cleaning, maintaining, repairing or replacing the lateral if necessary.

Cap sewer lateral cleanouts

Sewer lateral cleanouts should be capped so debris and rainwater cannot enter the sanitary system. If your cleanout cap is missing, find a replacement at a hardware store that carries plumbing supplies.

Release sump pumps outdoors

Sump pumps should discharge to the exterior of a building, away from structures to an area where water will not reenter the foundation. Sump pumps should not be connected to the sewer system.

Discharge stormwater connections to lawns

Gutters are intended to move rainwater from the roof of a structure and away from the building so that water does not enter the building. Other stormwater connections like foundation drains should not be connected to the sewer system.

An example of a video inspection of a private sewer lateral.
Video inspection.
An example of a properly capped sewer lateral cleanout.
Properly capped cleanout.
A properly configured outdoor downspout that discharges to vegetation and not the sewer system.
Downspout discharges to lawn.
A diagram showing the proper discharge of stormwater to a lawn via a downspout.
Proper stormwater discharge.
Driips Logo Primary

For more information on inflow and infiltration, learn about the regional DRIIPS program (Disconnect and Reduce Inflow and Infiltration to Private Sewers) to help educate property owners and reduce clear water in the sanitary sewers.

I&I Reduction Flyer