What is Inflow & Infiltration?
Inflow & Infiltration refers to the unintended entry of groundwater and stormwater into sanitary sewer systems. While they are often grouped together, inflow and infiltration are two distinct sources of excess water in the system.
Inflow occurs when water directly enters the collection system through improper or unauthorized connections. This can include open cleanouts, faulty or missing manhole covers, sump pumps, or drain spouts. Heavy rainfall and excessive surface runoff can also increase inflow.
Infiltration, by contrast, happens when groundwater seeps into the collection system through cracks, pipe defects, deteriorated joints, and other openings.
Infiltration tends to occur slowly, while inflow typically happens all at once – most often during periods of heavy rain or severe weather conditions.
Why is Inflow & Infiltration a critical issue for utilities?
I&I strains wastewater systems by increasing flow levels. When excess water enters the system, it reduces available capacity, increases the risk of sanitary sewer overflows, and places additional stress on treatment plants.
“In many cases, inflow and infiltration (I&I) accounts for up to 50% of the annual flow to treatment plants.”
This added volume means utilities may have to treat large amounts of clean water – an inefficient and costly process. Over time, this leads to:
- Higher operational and treatment costs
- Increased risk of sewer overflows
- Compromised water quality
- … and much more
It is estimated that I&I costs U.S. cities around $100 billion annually. This includes increased treatment and pumping costs, as well as costs associated with overflows, basement flooding, and potential litigation. More isolated a simple leak in a pipeline can cost as much as $10.000 in increased operational and treatment costs, why action is heavily needed.
These financial and operational challenges highlight just how essential it is for utilities to address I&I at its source. Left unchecked, persistent I&I can force utilities to invest in costly infrastructure upgrades, divert resources from other critical needs, and even lead to regulatory penalties. Beyond the fiscal burden, communities may face property damage, environmental degradation, and public health concerns when sewer systems are pushed beyond their limits.
Modern utilities are increasingly turning to advanced technologies and data-driven solutions to identify, quantify, and manage I&I more effectively. With a comprehensive understanding of where and how excess water is entering the system, utilities can prioritize repairs, optimize maintenance schedules, and allocate budgets more efficiently.
Did you know?
We have developed a specialist tool for wastewater utilities to combat I&I related issues – utilizing already existing data.