Optimizing Collection Systems: Advanced Solutions for I&I Challenges in Rural Communities

The best fix for inflow and infiltration in rural communities is a sequence, not a gadget. Size the problem from plant flow records you already keep, narrow the collection system to a few sewersheds, test only where the numbers point, and repair the sources that remove the most clear water first.

What is inflow and infiltration?

Inflow and infiltration (I&I) is clear water that rides to the plant with the sewage: groundwater seeping in through defects (infiltration) and rain and runoff entering through openings and connections (inflow).

EPA's construction grants rule, 40 CFR 35.2005, defines both. Infiltration enters from the ground through defective pipes, joints, connections or manholes. Inflow comes from roof leaders, yard and area drains, manhole covers, storm sewer cross connections, catch basins and similar sources.

Why is I&I a bigger challenge for rural communities?

Because the same few people run the plant, fix the mains and answer the night calls, with little spare capacity or money behind them.

EPA's America's Water Sector Workforce Initiative (October 2020) estimated that about one third of drinking water and wastewater operators would be eligible to retire within 10 years, and notes that rural areas and small towns can have particular trouble hiring and keeping staff. Even with funding in hand, someone still has to run the study and watch the work.

Capacity is the other squeeze. In Texas, measured plant flow, I&I included, drives the 75/90 rule in TCEQ's standard permit conditions for discharge permits, 30 TAC §305.126. At 75 percent of permitted flow for three consecutive months, the permittee must start engineering and financial planning to expand or upgrade. At 90 percent for three consecutive months, it must get TCEQ authorization to begin construction.

How do you size an I&I problem with data you already have?

Pull at least a year of daily plant influent flow, line it up with rainfall, and compare it to water billing. That shows whether you have an infiltration problem, an inflow problem or both.

EPA New England's Guide for Estimating Infiltration and Inflow (June 2014, archived by EPA) lays out the desk work:

• Divide plant flow by the sewered population. State screening standards run from 100 to 150 gallons per person per day. EPA's own 120 figure dates from 1985, when toilets used 3.5 gallons a flush, so it is a lenient line today.
• For infiltration, average the midnight to 6 a.m. flows over several dry days (three or more days without rain) at seasonal high groundwater, less any large industrial or commercial night flow.
• For inflow, compare storm flow with the dry weather flow just before it. Direct inflow rises soon after rain starts and drops fast. Delayed inflow tapers off slowly.
• Where every sewer customer has metered water, the gap between sewage flow and billed water in a low irrigation season estimates infiltration.

The guide adds that sewersheds served by pump stations that record flow can be analyzed the same way, using equipment you may already have.

How do you find where I&I enters without a big crew?

Find the sewersheds with the worst wet weather response and send people only there. Field tests confirm what the flow data suggests.

EPA's guide for evaluating CMOM programs (2005) describes temporary meters left in for 30 to 90 days and moved around to find high wet weather flow. It also notes meters may be expensive for a small owner, and that looking into manholes during low flow can be an effective, low cost check for a very small system.

• Smoke testing quickly finds inflow sources such as downspouts, yard drains and faulty service connections. Use it where excess I&I is already evident, in dry, calm daylight, with public notice first.
• Dyed water testing confirms connections and shows leaks around suspect manholes.
• CCTV gives a permanent record of cracks and joint defects inside the pipe.
• Routine manhole inspection, typically every one to five years, catches cracked barrels and leaky covers.

The CMOM guide also calls service laterals a serious source of I&I.

What technology solutions help a small utility?

Tools that turn readings into a short, ranked list. A map that ties every reading to a manhole ID does more for a small crew than a new device with no plan behind it.

The CMOM guide suggests building a geographic information system (GIS) early, then using it to track emergency calls and steer maintenance. Level sensors and lift station run time logs show when flow jumps between site visits. Aim for a few numbers per sewershed that a two-person crew can act on.

How do you prioritize I&I repairs on a tight budget?

Fix what causes overflows and backups first, then what removes the most clear water for the least work.

The EPA New England guide says I&I may be considered excessive when it causes overflows or bypasses, or when transporting and treating it costs more than removing it. It says building I&I work into the normal public works budget allows an incremental approach and can help defer capacity expansion.

Inflow sources are often quick wins: disconnecting a roof leader is a small job next to lining a main. Infiltration usually takes joint sealing, point repairs or lining. The CMOM guide asks whether rehabilitation happens before it becomes emergency maintenance, the proactive question every weekend call-out raises. Our guide to ranking and fixing your worst I&I sections goes step by step.

What do Texas rules say about I&I?

Texas expects new sewers to be designed for I&I and built tight.

• TCEQ's gravity pipe design rule, 30 TAC §217.53, requires design for peak flow plus infiltration and inflow, and a design that minimizes I&I.
• TCEQ's pipe testing rule, 30 TAC §217.57, requires new gravity pipe to pass a low pressure air test or an infiltration or exfiltration test, with exfiltration capped at 10 gallons per inch of diameter per mile of pipe per 24 hours.
• TCEQ's manhole testing rule, 30 TAC §217.58, requires every manhole to pass a leakage test, with hydrostatic leakage capped at 0.025 gallons per foot of diameter per foot of depth per hour.
• TCEQ's Sanitary Sewer Overflow Initiative, a voluntary program since 2004, names significant inflow and infiltration as an overflow cause. Public systems not already under formal enforcement for overflows can join, and are then not subject to formal TCEQ enforcement for most continuing overflows their plan addresses. EPA can still act.

How should a small town get started?

Check what you already have. If you can answer yes to the first three, you can size the problem now; the rest help narrow it. If not, closing those gaps is step one.

1. Do you have 12 months of daily plant influent flow?
2. Do you have daily rainfall for the same period?
3. Do you know the sewered population or connection count?
4. Do your lift stations record flow or pump run times?
5. Is there a current map of mains and manholes with field IDs?
6. Do you log overflows, backups and emergency calls by location?

Then ask your engineer which sewersheds jump most in wet weather, whether it is mostly inflow or infiltration, and which repairs remove the most flow for the work. More on planning for small systems is on our page for utilities and municipalities.

A note on limits: this is general education from public sources, current as of October 2026. Texas rules apply in Texas, other states set their own, and your engineer and the reviewing agency have the final word.

Frequently asked questions

How much infiltration is too much?

Compare plant flow per person with your state's screening standard. Above it, a fuller analysis usually follows. I&I that causes overflows counts as excessive whatever the per person number.

Can smoke testing get into houses?

It can. The CMOM guide notes that smoke or its odor inside a building means sewer gas may be getting in too. That is why public notice comes first.

I'm the public works director for a small Texas town with one licensed operator, and our plant flow jumps every time it rains. Where do we start on I&I without adding staff?

Start at a desk. Pull a year of daily influent flow and rainfall. A fast spike that drops quickly points to inflow. Use lift station flow records to split the town into sewersheds, check manholes at night in dry weather, and smoke test the worst wet weather sewershed first.

I manage a Texas utility district whose plant hit 75 percent of permitted flow during three wet months in a row. Can fixing I&I put off an expansion?

It can help, but it does not cancel the rule. 30 TAC §305.126 still requires planning, unless TCEQ waives it in writing on an engineering report. EPA New England's guide says steady I&I correction can help defer expansion. How much it buys depends on how much of your peak is clear water, so size that first.

Related resources

• Key Take Aways From EP11: How Inflow and Infiltration Impacts Your Collection System and Wastewater Treatment Plant
• Understanding Your Community's Wastewater Collection System
• Knowing When Your Wastewater Treatment Plant (WWTP) Needs to be Upgraded: A Guide for Rural Communities
• Capital Improvement Planning for Small Municipalities

Chasing I&I with a small crew?

Send us a year of plant flow, your rainfall record and a system map. We will help you size the problem, pick the sewersheds worth testing and turn the results into a repair list your crew can work through.

Modern Engineering Solutions, McKinney, Texas, with offices in Golden, Colorado and San Jose, California. 525+ projects completed.

Talk to an engineer about your collection system or call (214) 833-6748.