Infiltration-Inflow (I/I)

Infiltration & Inflow Reduction Program

In a continuing effort to meet the standards of the Clean Water Act of 1972, maintain current sanitary sewer operating costs and/or reduce those costs, and to safeguard the Lake Erie watershed the
Ottawa County Sanitary Engineering Department, along with the Ottawa County Commissioners, have implemented an infiltration/Inflow (I&I) Reduction Program. The program’s goals are to identify both public and private points of entry by ground/rain water into the sanitary sewer system, to proactively educate the public about I & I, work with property owners to address potential violations, and to maintain the integrity of the publicly owned collection system to protect the environment. Additionally, during heavy rain events, excess amounts of Infiltration & Inflow can cause sanitary sewers to fill beyond their designed capacity producing backups into private residences.

What is Infiltration & Inflow?

Infiltration and Inflow, more commonly referred to as I & I, is the introduction of ground/rain water into the sanitary sewer system. Both infiltration and inflow can occur in a variety of ways which are detailed in the descriptions below.

Infiltration is water, other than wastewater, that enters a sewer system (including sewer service connections and foundation drains) from the ground through such means as defective pipes, pipe joints,
connections or manholes. Infiltration does not include, and is distinguished from, inflow. 
Infiltration quantities often change depending on the season, groundwater levels, and lake or river levels.

Heavy rain events can trigger a rise in groundwater levels and increase infiltration. The highest infiltration flows are observed following significant storm events or following prolonged periods of

Inflow is water, other than wastewater, that enters a sewer system (including sewer service connections and foundation drains) from sources such as, but not limited to, roof leaders, cellar drains, yard drains, area drains, foundation drains, field tile, drains from springs and swampy areas, manhole covers, cross connections between storm sewers and sanitary sewers, catch basins, cooling towers, storm waters, surface run-off, street wash water, or drainage. Inflow does not include, and is distinguished from, infiltration. Inflow occurs as a result of events such as rainfall, snowfall, springs or snow melt all of which contribute to excessive sewer flows.

In the graphic below, sources of I/I are illustrated.


Ascertaining Sources of I & I

There are numerous ways in which infiltration and inflow can be discovered within the sanitary sewer system and they include smoke testing, flow monitoring data, robotic camera inspections, dye testing, periodic inspections of the public sewer, and customer concerns.

Smoke Testing


Ottawa County Sanitary Engineering Department’s I & I Reduction Program performs smoke testing to detect deficiencies within the sanitary sewer system. Non-toxic smoke is blown into the sewer system, which then travels through the sewer system and escapes through any connection, cracks, leaks, etc., identifying points of inflow or infiltration. Residents will be notified at least two (2) weeks in advance via US Mail of smoke testing in the area of their residence and then again with door hangers 24-48 hours
prior to the actual testing day (weather depending).

Smoke Testing FAQ
Sample Letter
Sample Door Hanger

Flow Monitoring


Robotic Camera (CCTV)


Dye Testing


Customer Concerns


What Can You Do To Help?

With the aid of customers, the Ottawa County Sanitary Engineering Department can continue to keep sewer treatment plant and operational/maintenance costs low by eliminating infiltration and inflow from being introduced to the system. Below are a few ways that you can assist us in eliminating I & I.

  •  Have your private sewer lateral inspected and repaired, if need be, by a registered contractor.
  • Report any suspected I & I issues to the Sanitary Engineers office.
  •  Ensure your cleanout is properly capped.
  • Stormwater connections such as roof drain downspouts, yard drains, and sump pumps can be disconnected from the sewer system. You can redirect the downspouts onto lawn and garden
    beds, hook up a rain barrel or cistern to their downspouts, or redirect the connections to a separate stormwater system.


For more information regarding
Infiltration & Inflow please contact:

Ryan Barth, SSES Coordinator
[email protected]