Inflow & Infiltration

What is Inflow & Infiltration?

Water that flows into a dedicated sanitary sewer system from groundwater or storm water is called inflow and infiltration (I/I). Sanitary sewers are strictly designed to transport wastewater from sanitary plumbing fixtures, such as toilets, sinks, bathtubs and showers.

man fixing pipe under sink
spout in yard with catch basin


Inflow occurs from surface water sources that flow directly into the sanitary sewer via a defined route from cross-connections with storm drains, downspouts, and through holes in manhole covers.

Inflow occurs as a result of storm events such as rainfall, snowfall, or snow melt that contribute to excessive sewer flows. Peak inflow can occur during heavy storm events.

water leaking into pipe


Infiltration is groundwater that inadvertently enters into the sanitary sewer system through holes, breaks, joint failures, connection failures and other openings.

Infiltration quantities often exhibit seasonal variation in response to groundwater levels. Storm events can trigger a rise in groundwater levels and increase infiltration flows.

With the help of the Ohio EPA, The District began to implement a public/private Inflow and Infiltration program that will help reimburse homeowners with a portion of the construction costs. Visit our Inflow & Infiltration Homeowner Assistance Program page to learn more.

Sources Of Inflow & Infiltration

Private Inflow Sources

Private land areas (outside of public right-of-way) inflow sources include roof downspout connections, yard and driveway drains, broken or missing sanitary lateral cleanout caps, and sump pump connections to the sanitary sewer system.

These connections are illegal and can add thousands of gallons of storm water into the sanitary sewer system per household during large rain events. Inflow sources are usually easy to remediate.

Public Right of Way Inflow Sources

Inflow sources within the public right-of-way can include sanitary manhole covers and storm water catch basins that are inadvertently tied into the sanitary sewer.

Private Infiltration Sources

Private infiltration sources can include broken lateral sewers, faulty lateral connections, tree root penetration, and broken cleanouts.

sources of inflow and infiltration and a properly connected sewer system

How We Find the Sources

Smoke Testing

Involves pumping smoke through sewers from manholes in streets and observing where smoke exits.

The exiting smoke can indicate a broken pipe or identify where roof or foundation drains are improperly connected to the sewer system.

man filming smoke testing
camera inspection in pole

Camera Inspections

Cameras can be robotically sent down sanitary sewer lines and along each side sewer to record a video of sewer conditions.

Inspections can identify breaks, root intrusion, leaking water, and deteriorating conditions.

Dye Testing

Involves pouring non-toxic fluorescent colored dye down roof drains or catch basins to see if that dye makes its way into the sewer.

This provides verification that the storm drainage being tested is directly connected to the sewer.

dye testing in pipe

Fixing Inflow & Infiltration

Redirecting Your Downspouts

Each downspout on a house can drain approximately 12 gallons of water per minute during a one-inch rainfall. Downspouts that connect directly to the sanitary sewer system increase the risk of sewer overflow and flooding.

Disconnecting your downspout from the sanitary sewer and redirecting the flow is a simple process that can make a big difference. Redirecting a downspout into a rain barrel and with an elbow and extension into the yard.

Backflow Preventer

A mechanical valve or a check valve will help prevent basement flooding. A check valve that closes automatically when flow through the sewer line reverses may be installed either outside the house or inside the basement, depending on the plumbing configuration of your home.

These backflow devices are very effective in eliminating back-up. However, they can sometimes become clogged with debris and fail to close completely. When this happens, the valve will slow down the flow of sewage but not stop it completely. For this reason, the valve should be accessible for service and repair.

Basement Plumbing

The first step in preventing basement flooding is to understand how your basement is designed. The diagram illustrates proper connections to the storm sewer and sanitary sewer system. The floor drain and waste from the bathrooms and kitchen are going out through the sanitary sewer and the sump pump and downspout are discharging to the storm sewer.

Storm water improperly discharged into a sanitary sewer can causing basements to flood into homes . The saintary sewer was designed to handle the sanitary waste only and does not have the capacity to handle the additional flow of storm water.

Submersible Sump Pump Installation

Find your sump pump. If the sump pump is connected to any other pipe in your home, it is most likely improperly connected. The drainage pipe from your sump pump should go from the pump directly outside your home at ground level. When a sump pump is re-plumbed to pump ground water to the yard or storm sewer, that water no longer takes up space in the sewer system.