Protect The Lateral·7 min read
Inflow and Infiltration: Why Your Cracked Lateral Floods the Main
Inflow and infiltration · usually shortened to I&I · is the clean groundwater and stormwater that leaks into a sanitary sewer system through defects it was never meant to carry. It's one of the biggest hidden strains on municipal sewer systems, and a surprising share of it comes from private laterals on individual homes.
If your lateral is cracked, has open joints, or has been invaded by roots, it's not just a backup risk. It's an open door for groundwater to pour into a system that's supposed to carry waste only. Here's how that works and why it's worth fixing before the city makes you.
Inflow vs. infiltration · the difference
The two halves of I&I get lumped together, but they enter the system differently.
- ·Infiltration · groundwater seeping in slowly through cracks, bad joints, and root-damaged sections of pipe, especially when the water table is high.
- ·Inflow · stormwater that rushes in directly through improper connections like downspouts, sump pumps, or uncapped cleanouts tied into the sanitary line.
Why I&I overloads the main
A sanitary sewer is sized to carry wastewater, not rain. When thousands of homes each leak a little groundwater through failing laterals, those small leaks add up to a flood inside the main during wet weather.
An overloaded main backs up · into basements, into streets, and into treatment plants that have to process diluted sewage they were never sized for. That's why municipalities increasingly inspect private laterals and issue notices to homeowners whose pipes are leaking into the system.
Your lateral is often the source
Cities have spent decades sealing their own mains, which means the remaining I&I increasingly traces back to the private side · the laterals homeowners own and rarely think about. A single cracked lateral in saturated soil can take on a remarkable amount of groundwater.
The fix is to find the defects and seal them: spot repairs, joint sealing, or trenchless lining that restores a continuous, watertight pipe from the house to the main. Step one is always seeing where the water gets in.
Proving the line is sealed
Whether you're acting before a problem or responding to a city notice, the win condition is the same: a documented, watertight lateral. A camera inspection finds the defects, the repair seals them, and a follow-up run proves the line is locked in.
Operators running FieldMetrx™ capture that before-and-after on the spot · the defect footage, the recommended fix, and the proof the line is sound · so you have a record that satisfies you and, if needed, the city. That documentation is the whole point: an unsealed lateral is a liability, a proven one is a closed file.
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Claim Your SpotFrequently asked
What does inflow and infiltration mean?
It's the clean groundwater (infiltration) and stormwater (inflow) that leaks into sanitary sewer pipes through cracks, bad joints, and improper connections · water the system was never meant to carry.
Why is I&I a problem for homeowners?
A leaking lateral overloads the public main and can trigger a city repair notice. It also signals that your pipe has defects that can lead to backups into your own home.
How do I stop infiltration into my sewer lateral?
Locate the defects with a camera inspection, then seal them with spot repairs, joint sealing, or trenchless lining to restore a continuous watertight pipe. A follow-up camera run confirms the seal.