About Inflow & Infiltration
Inflow and Infiltration Definitions
Storm sewers are designed to convey rainwater and groundwater. Sanitary sewers are designed to convey domestic wastewater, such as water from toilets, sinks, washing machines and showers. If rainwater or groundwater enters the sanitary sewer system, it is referred to as inflow and infiltration (I&I), respectively.
Inflow: Rainwater that enters the sanitary sewer through holes in manhole covers, catch basins or improper plumbing connections.
Infiltration: Groundwater that seeps into the sanitary sewer through cracks or joints in the sewer pipe.
Typically, I&I enters the sewer system through sources on both public roads and private properties via cracked pipes, leaky manholes or improperly connected storm drains and roof gutter downspouts. Current studies indicate that 50% of I&I comes from sources on private property.
To effectively manage sanitary sewers, various I&I reduction strategies are available. Public property I&I reduction strategies involve methods which reduce I&I into the manholes, sewer mains and service laterals within the public rights-of-way. Private property I&I reduction strategies involve methods to reduce I&I coming from the homeowner’s property.