The Impact of Excess Rainfall

Inflow and Infiltration (I&I)

What is I&I?

Excess water that flows into sewer pipes from stormwater and groundwater is called inflow and infiltration, or I&I. Stormwater rapidly flows into sewers (inflow) via roof drain downspouts, foundation drains, storm drain cross-connections, and through holes in manhole covers. Groundwater (infiltration) seeps into sewer pipes through holes, cracks, joint failures, and imperfect connections. Most I&I is caused by aging infrastructure that needs maintenance or replacement.

Why It Matters

ECUA has committed considerable resources to the elimination and reduction of sewer inflow and infiltration (I&I) in the last three fiscal years. This is an issue that affects, and is of great concern to wastewater utilities throughout North America. ECUA has laid out a 15-year plan to address the situation. Protecting public health and the environment – and reducing wastewater treatment and transmission costs are direct benefits of a regional I&I control program.

3 Reasons Why I&I is a Problem

Extra water in the sewer system is a problem because:

I&I flows contribute to sewer system overflows into local homes and the region’s streets and waterways, negatively impacting public health and the environment.

It takes up capacity in the sewer pipes and ends up at the water reclamation facilities where it must be treated like sewage, increasing treatment costs.

Over time, new and larger wastewater facilities are required to convey and treat larger volumes of flow, resulting in higher capital and operating expenditures.