Quick answer
A catch basin is a box or pit with a grate on top that collects surface runoff, lets sediment settle in a sump below the outlet pipe, and passes the clearer water on through a pipe.
It is a collection and settling point, not a treatment plant or a place where water soaks in. Without regular cleaning, the sump fills and the basin stops doing its job.
Quick facts
The key facts about Catch Basin, with sources:
- What it is
- A storm drain inlet with a grate or curb opening and a sump 1
- Sump
- A space set lower than the outflow pipe where sediment settles 2
- Iowa sump depth
- A minimum 12 inches is recommended 2
- Iowa cleaning trigger
- Remove sediment when half the sediment space is full 2
- What it will not do
- Remove dissolved pollutants or fine particles effectively 1
Key takeaways
- A catch basin collects water at one point and lets heavy sediment drop into a sump before the water moves on.
- It is pretreatment, not a cure. Connecticut’s manual says even well-designed basins are far less effective than primary stormwater practices.
- The sump has to be emptied. Iowa suggests removal when half the sediment space is full, which it expects to be once or twice a year in its example design.
- You can check the lid, grate and inlet from the surface. Do not enter the structure; confined-space rules apply.
- Where the basin sends its water is the legal question. Storm drains lead to local waters untreated, per EPA.
A catch basin in plain English
Picture a bucket set into the ground under a grate. Rain runs across a driveway or lawn, drops through the grate and into the bucket. Heavy grit sinks to the bottom. The water leaves through a pipe set higher up, so the sediment stays behind.
Connecticut’s stormwater manual describes catch basins as “storm drain inlets” with a grate or curb inlet and a sump. They trap trash, debris, some sediment, and oil and grease.
Floatables stay on a permanent pool and coarse sediment settles into the sump 1.
The Iowa Stormwater Management Manual says the sump is “set lower than the outflow elevation,” so water pools in the bottom and lets sediment and debris settle out 2.
The word covers a lot of ground. A homeowner’s “yard drain” or “area drain” is a small catch basin, often a plastic box. A street inlet is a large one owned by the city. They share the same idea: collect at a point, settle, pass on.
Kinds of catch basin and what each is built to do
| Kind | What it is | Source note |
|---|---|---|
| Basic inlet with a grate | Collects runoff and may have a sump | Connecticut: a storm drain inlet with a grate or curb inlet and a sump 1 |
| Deep sump catch basin | A basin with a larger sump to hold sediment | Also called an oil and grease catch basin in Connecticut 1 |
| Hooded catch basin | An inverted pipe or tee on the outlet keeps oils and floating debris suspended on the water trapped in the sump | Connecticut and Iowa describe the hood 12 |
| Basin with a trash screen | A screen over the outlet keeps larger trash inside | Iowa notes the designer should consider maintenance frequency and clogging of the screen openings 2 |
| Basin with weep holes | Small holes let collected water slowly infiltrate into a rock chamber below an adjacent practice | Iowa gives this as an alternative to a permanent pool 2 |
Catch basin, area drain and storm drain inlet are close cousins
All three collect water at a point. Who owns the structure and where its outlet goes decide the rules, so ask your city whether a basin on your lot connects to a public storm system.
How a catch basin handles one rain
The flow is simple, and each step explains a maintenance need.
- Water runs to the grate. A paved or graded surface sends runoff toward the opening.
- Debris stops at the grate. Leaves and trash can block the inlet and slow the flow.
- Sediment drops into the sump. Iowa says the sump captures coarse sediments, debris and oils in a confined location where they can be collected and removed 2.
- A hood or elbow holds back floating material. It keeps oils and floating debris on top of the water in the sump 2.
- Cleaner water leaves through the outlet pipe. It goes to a storm system, a daylight outlet or another practice.
- Grate and frameLets water in and keeps people and large debris out
- Inlet pipe or surface openingWater enters here
- Hood or downturned pipe on the outletKeeps oils and floating debris in 2
- Outlet pipeCarries water on
- Sump below the outlet pipeHolds settled sediment; Iowa recommends at least 12 inches 2
A schematic of the idea in the Iowa and Connecticut manuals. Sizes come from the design for your site. Source: [2] [1]
Example: when a catch basin needs attention, in numbers
The City of Gig Harbor, Washington, publishes a maintenance checklist for catch basins in its stormwater manual (December 2016), and Iowa’s manual sets a cleaning trigger. These thresholds are for public and commercial systems in those places. They are not rules for your yard, but they show what a professional looks for 32.
| What is checked | Trigger for maintenance | Source |
|---|---|---|
| Trash or debris in front of the opening | Blocking inlet capacity by more than 10 percent | Gig Harbor 3 |
| Grate surface blocked by trash or debris | More than 20 percent of inletting capacity | Gig Harbor 3 |
| Vegetation across the basin opening | Blocking more than 10 percent | Gig Harbor 3 |
| Sediment in the basin | More than 60 percent of sump depth, never leaving less than 6 inches of clearance below the lowest pipe | Gig Harbor 3 |
| Sediment collection space (Iowa pretreatment sump) | Remove when 50 percent of the capacity is filled | Iowa 2 |
| Grate opening | Wider than seven-eighths of an inch is unsafe | Gig Harbor 3 |
| Cover | Missing or only partly in place: any open catch basin requires maintenance | Gig Harbor 3 |
Two lessons follow. The surface checks, the first three rows and the cover, can be done by anyone from above ground. The sump and structural checks need a trained crew, since Iowa notes that people entering the below-ground part are typically required to be certified through confined space training 2.
Where you meet catch basins: driveways, patios and drainage bids
You find catch basins at the low point of a driveway, in a patio or courtyard, at the bottom of a sloped yard, and along the street. In a bid, they appear as “yard drain,” “area drain” or “drain basin,” often with a pipe run to a daylight outlet or the street.
Ask three questions of any bid that includes one. Where does the outlet go, and who approved it? How is the sump emptied, and by whom? Is there a hood or screen? The drainage and grading service page explains what a full drainage job includes.
A catch basin often sits next to a patio or walkway, where water has nowhere else to go. In that case, grading and the basin work together. See hardscape base specification for how paving is built to shed water.
Photograph it after install
Take a photo of the open basin, the outlet pipe and the cover before backfill is finished, and note the 811 ticket. A record helps the next owner and any cleaning crew.
What a catch basin does well
Where it helps
Limits: small capacity, no treatment and a place to put the water
Iowa’s manual says catch basin sumps and inserts have limited capacity and are best suited to smaller watershed areas.
They are pretreatment devices only, and without a maintenance plan they fill up and stop working until cleaned out 2.
Connecticut adds that even well-designed basins are “far less effective at removing pollutants than primary stormwater management practices” 1.
A basin also does not make water disappear. It moves water to its outlet. EPA says runoff from roads and rooftops that enters storm drains travels untreated to streams, rivers, lakes and the ocean, carrying fertilizer, oil, pesticides, dirt and bacteria 4. So the outlet matters as much as the box.
Finally, a basin is not a grading fix. If water pools because the ground slopes toward a house, the answer begins with landscape grading, and the basin is a secondary tool.
What drives the cost of a catch basin, and how long one lasts
We do not publish prices. A bid moves with the size and material of the basin, the sump depth, the grate type, the depth and length of the pipe to the outlet, excavation and hauling, any hood or screen, and surface restoration.
Utility conflicts found by 811 can change the route. Cleaning is a recurring cost. Iowa says the sump typically needs removal once or twice a year in its design, and a vacuum truck may be needed 2.
We found no source giving a lifespan or warranty for a residential catch basin, so we do not offer one. Ask the installer for what the product and the work are covered for. For the wider budget picture, see the cost guide and how to read landscaping estimates.
Who installs it, and the order of steps
A homeowner can plan a small yard basin, but many go to a drainage contractor. A connection to a public storm system usually needs approval. Permits and inspections vary by city.
- Ask your city or county what the outlet may connect to, and whether a permit is needed.
- Plan the grade. Water must reach the basin and leave it by gravity.
- Call 811. USA North 811 says to pre-mark the area, call at least two working days before digging and wait for each utility to respond 5.
- Choose the basin features: a sump, a hood or screen, and a grate rated for the traffic it will face.
- Install and test with water before the area is finished.
- Set up cleaning. Iowa says to name the party responsible for maintenance and keep a path clear for the vacuum truck 2.
Stay out of the structure, and keep the cover on
Iowa’s manual says people entering the below-ground part of these structures are typically required to be certified through confined space training 2. Gig Harbor’s checklist lists dead animals or vegetation that could generate dangerous gases such as methane as a maintenance trigger 3.
Do not climb in, and report a missing cover to the owner or city. Call 811 before any digging 5, and never send overflow onto a neighbor’s land or into a sanitary sewer.
Keeping a catch basin working
- Clear the grate and inlet of leaves and trash from above. Gig Harbor treats more than 20 percent grate blockage as a trigger 3.
- Inspect on a schedule. Iowa says at least four times in the first year and at least twice a year after, more often if sediment builds up 2.
- Have the sump emptied when about half of the space is full 2.
- Dispose of the solids properly. Iowa says sediments from areas that are not hotspots are not currently considered toxic or hazardous, but guidance on PFAS is evolving and testing may be required for hotspots 2.
- Keep chemicals out. See lawn chemical safety for what not to let reach a drain.
Warning signs, and when to call a professional
- Water ponds around the grate after rain. The inlet or the sump may be full.
- The cover is missing or cracked. Gig Harbor says any open catch basin requires maintenance 3.
- Cracks wider than one-fourth inch in the top slab, or holes larger than 2 square inches 3.
- A sheen, odor or oil in the basin. Gig Harbor lists oil, gasoline or other contaminants as a trigger 3.
- Standing water in the basin that breeds mosquitoes. Connecticut notes the risk 1.
Structural or sump problems are a job for a drainage contractor or the city. If you are unsure whether there is a problem, Gig Harbor’s checklist advises contacting a professional engineer 3.
Rules and standards that apply
No single national code governs a yard catch basin. The figures in this page come from design manuals: Connecticut’s Stormwater Quality Manual (the deep sump chapter is dated 2004), Iowa’s Stormwater Management Manual (section 5.06, issued September 24, 2024), and a city checklist from Gig Harbor, Washington (December 2016) 123.
Manuals are guidance for designers. A city code or permit is the binding rule where it applies.
Three kinds of rule matter in practice. Ownership and connection: a city or county sets what may connect to its storm system.
Digging: state 811 laws require you to call first, and USA North 811 says at least two working days before digging, though your state may differ 5. Water leaving your lot: state drainage law and local rules on neighbors differ.
See French drain for a summary of the three drainage-law doctrines and why you should ask a local attorney.
Grate openings and covers may have their own safety rules. Gig Harbor’s checklist flags grate openings wider than seven-eighths of an inch as unsafe 3. Local codes decide what applies to a yard.
Catch basin compared with other drainage tools
| Tool | What it does | How it differs from a catch basin |
|---|---|---|
| Catch basin | Collects surface water at a point and settles sediment 2 | The baseline here |
| Channel drain | Collects water along a line, such as across a driveway | Linear; a basin is a single point |
| French drain | Collects soil water along a gravel trench | Takes soil water; a basin takes surface water |
| Dry well | Lets piped water soak into the ground | Infiltrates; a basin passes water on |
| Downspout extension | Moves roof water away from a wall | No box or sump |
| Storm drain inlet in the street | Usually a public catch basin | The same idea at street scale; ask your city who maintains it |
Catch basin myths
- Myth A catch basin cleans the water.
- Reality Connecticut says it cannot effectively remove soluble pollutants or fine particles 1.
- Myth Once installed, it needs no care.
- Reality Iowa says the sump must be emptied; without maintenance it fills and stops working 2.
- Myth Storm drains go to a treatment plant.
- Reality EPA says runoff in storm drains travels untreated to streams, rivers, lakes and the ocean 4.
- Myth I can open the cover and climb in to clean it.
- Reality Iowa says entry into the below-ground part typically requires confined space certification 2.
- Myth The outlet can go to the nearest ditch or the neighbor.
- Reality Where it goes is a legal question; ask your city before you connect.
Your city’s stormwater rules decide the details
The regional variable is your local stormwater system and code. Iowa recommends a 12-inch minimum sump, while Gig Harbor’s checklist flags sediment at 60 percent of sump depth 23. Both are local or state design guidance, not national rules.
Cities differ in what they allow to connect, who owns the basin and what is inspected. Your city or county stormwater office has the current requirements, and our soil drainage research shows where yards flood.
When a catch basin makes sense, and the next step
A catch basin makes sense at a low point where surface water gathers, when there is a lower legal outlet, and when someone will clean the sump. It makes less sense when the cause is poor grading, soil water, or no outlet.
Your next step is to find where the water comes from and where it can go. Use the drainage diagnostic and ask your city about outlets. If you hire a company, see how to choose a landscaping company.
- If Water gathers at a low point on pavement or lawn
- Then A basin with a lower legal outlet may fit
- If Water is rising from the soil
- Then Look at a subsurface drain instead
- If No lower outlet is available
- Then A basin will only move the pond; consider other designs
- If No one will clean the sump
- Then Skip it, or add a plan. Iowa says maintenance is essential 2
Questions about Catch Basin
What is a catch basin?
A catch basin is a box or pit with a grate that collects runoff and lets sediment settle in a sump before water leaves through an outlet pipe. Connecticut’s manual describes catch basins as storm drain inlets with a grate or curb inlet and a sump that trap trash, debris, some sediment, oil and grease.
What is the difference between a catch basin and a storm drain?
A storm drain is the whole system of inlets and pipes that carries runoff. A catch basin is the inlet structure with a sump, one part of that system. EPA says storm drain water usually travels untreated to local waters, so the basin collects, but does not clean, what it passes.
How does a catch basin work?
Water enters through the grate, heavy sediment settles into a sump set lower than the outlet pipe, and the water leaves through the outlet. Iowa’s manual says the sump captures coarse sediments, debris and oils in a confined location where they can be removed. A hood can keep oils and floating debris in.
How deep should a catch basin sump be?
Design guidance varies. Iowa’s Stormwater Management Manual recommends a minimum sump depth of 12 inches, with more as needed to provide the desired pretreatment volume. Connecticut’s deep sump page gives no number. A designer sets the depth for your site and local rules.
How often should a catch basin be cleaned?
Iowa’s manual says to inspect at least four times the first year and at least twice a year after, and to remove sediment when 50 percent of the collection capacity is full, which it expects to be once or twice a year.
Gig Harbor’s checklist triggers at 60 percent sump fill. Your local rules and site decide.
Can I clean a catch basin myself?
You can clear leaves and trash from the grate and inlet from the surface. Emptying the sump and entering the structure are different. Iowa says personnel entering the below-ground part are typically required to be certified through confined space training. Hire a trained crew, and report a missing cover to the owner.
Where should a catch basin drain to?
To a lower, legal outlet, such as a daylight point on your property or a public storm system with permission. Never to a neighbor’s land or a sanitary sewer. Ask your city or county what your outlet may connect to, because rules on connections and ownership vary.
Does a catch basin filter pollutants?
Only coarse ones. Connecticut says catch basins cannot effectively remove soluble pollutants or fine particles, and are far less effective than primary stormwater practices. Sediment can be resuspended and floatables can pass downstream in large storms. Think of it as pretreatment.
Do I need to call 811 before installing a catch basin?
Yes. Any digging calls for it. USA North 811 says the service is free, to pre-mark the area, to call at least two working days before digging and to wait until every utility has responded. Your state’s notice period may differ.
Is a catch basin the same as an area drain?
Often, yes. “Area drain,” “yard drain” and “drain basin” usually mean a small catch basin set at a low point in a yard, patio or driveway. The basics are the same: a grate, a box, and an outlet pipe. Ask any bidder to describe the sump, the hood and the outlet.
Sources
- Connecticut Stormwater Quality Manual (UConn NEMO with CT DEEP), Deep Sump Catch Basins (2004), retrieved .
- Iowa Stormwater Management Manual, Section 5.06 Catch Basin Sumps and Inserts (issued Sept. 24, 2024), retrieved .
- City of Gig Harbor, Washington, Stormwater and Site Development Manual, Vol. I, Appendix A, Maintenance Checklist for Catch Basins (Dec. 2016), retrieved .
- US EPA, Soak Up the Rain: What’s the Problem?, retrieved .
- USA North 811, DIYers (call 811 before you dig), retrieved .
Expert review
Written by the HyreYard Research Desk. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Definitions, sump and hood features, and maintenance triggers were read on the cited state and city manuals on 2026-10-14.
The Iowa and Gig Harbor figures are design and maintenance guidance for public or commercial systems and are labeled as such, not as rules for a yard. Two of the sources were read from PDF text. No design, size or schedule is given for every yard.
Suggest a correction. We fix errors and say what changed.