Infiltration & Inflow

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 and Inflow can cause sanitary sewers to fill beyond their designed capacity producing backups into private residences.

Infiltration & Inflow Explained

Infiltration and Inflow, more commonly referred to as I and 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 precipitation.


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.

Ascertaining Sources of Infiltration & Inflow

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 weeks in advance via U.S. mail of smoke testing in the area of their residence and then again with door hangers 24 to 48 hours prior to the actual testing day, weather depending.

How You Can Assist with Infiltration & Inflow

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.

  • Ensure your cleanout is properly capped
  • Have your private sewer lateral inspected and repaired, if need be, by a registered contractor
  • Report any suspected I and I issues to the Sanitary Engineers office
  • Storm water 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

More Information

For more information regarding Infiltration and inflow please email Ryan Barth, Deputy Director or call 419-734-6725.