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Infiltrations and Inflow (I/I)

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The privately-owned portion of the sewer pipeline that connects your home to the public sewer main is called the sewer lateral. Two major issues with sewer laterals can cause significant excess flows of water, which may lead to sewer backups and spills. These two issues are called infiltration, and inflow.

Infiltration: Over time, sewer laterals age and deteriorate, crack, leak, and break. During wet weather, massive amounts of storm water percolate into the soil, where it enters the cracks in the sewer lateral and mixes with the sewage flow.

Inflow: This is an illegal connection to a property’s sewer lateral, such as sump pump discharges or gutter downspouts, bringing excess water into the sewer system.

Both infiltration and inflow (also known as I/I) cause unnecessarily high flows in the sewer main network. That additional water coming into the system can overwhelm sewer pipelines, and lead to potential spills and backups into homes, streets, and the Bay.  Excess flows of water to the treatment plant require the facility to process the higher flows at increased costs for power and chemicals. Laws and regulations mandate zero tolerance for sewer overflows and spills, and failure to stop them brings stiff fines and legal actions.

The Sewer Lateral Assistance Program and Sewer Lateral Ordinance are two ways the District is addressing the problems of infiltration and inflow.

Repair or replacement of a sewer lateral is the responsibility of the property owner. The District’s Sewer Lateral Assistance Program provides low-interest loans to help pay for sewer lateral replacement – click here for more information and to apply. You can also learn more about this critical issue and what you can do to help, in this summary on I/I and its environmental impacts (provided by Bay Area Clean Water Agencies – BACWA).

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summary on I/I and its environmental impacts

Information on the Sewer Lateral Ordinance

Overview of Sewer Lateral Ordinance – FlyerSewer Lateral Inspection and Report FormNew Sewer Lateral Ordinance – Ordinance 180


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