Short answer: Start with an official lookup: Suffolk's septic-grant eligibility map shows whether an address is sewered or in a proposed sewer district, and Nassau's health department publishes a list of communities that are not publicly sewered. If you're not on sewer, the house has a cesspool, a septic system or an I/A system; the questions below narrow it down, and an operator confirms it when the covers come off.
Last updated: November 2026.
Step 1: check sewer status
- Suffolk: the county's SIP eligibility lookup (built for the grant program) reports sewer and proposed-sewer status by address. Our Suffolk town pages show the share of each hamlet inside an active or proposed county sewer district, measured on the county's GIS layer. Some village systems (for example Greenport and Sag Harbor) are not in that county layer.
- Nassau: most communities are served by the county Department of Public Works or a local water pollution control district. The county health department's list marks these as not publicly sewered:
- Bayville
- Brookville
- Centre Island
- Cove Neck
- East Hills
- East Norwich
- Flower Hill (western part)
- Glen Head
- Glenwood / Glenwood Landing
- Great Neck Estates
- Greenvale
- Kings Point
- Lattingtown
- Laurel Hollow
- Locust Valley
- Manhasset
- Matinecock
- Mill Neck
- Munsey Park
- Muttontown
- Old Brookville
- Old Westbury
- Oyster Bay Cove
- Plandome
- Plandome Heights
- Plandome Manor
- Roslyn Estates
- Roslyn Harbor
- Roslyn Heights
- Sands Point
- Sea Cliff
- Split Rock
- Upper Brookville
Source: Nassau County Department of Health, public sewer collection districts by community. The list is by community, not by street; parts of some communities differ.
Step 2: five questions
What each system is
| System | How it works | What you'll see |
|---|---|---|
| Cesspool | A buried chamber that receives raw waste and leaches the liquid into the soil; solids stay inside and need pumping. Older ones were built of cement block or brick. | One or more round covers, often buried |
| Conventional septic | A septic tank where solids settle and grease floats, then a leaching structure (on Long Island, usually a leaching pool) for the clearer effluent | A tank cover plus ring covers |
| I/A system | A treatment tank that removes nitrogen biologically before the water goes to the leaching structure | Covers at grade, a control panel with an alarm, vent piping |
| Public sewer | Wastewater leaves the property through a sewer main to a treatment plant | A cleanout near the house; a sewer charge |
Suffolk has barred cesspools in new construction since 1973 (SCDHS, 11/19/2024 presentation), and since July 1, 2019 a cesspool can't be replaced with another cesspool. So the house's age and whether the system has been replaced since 2019 are good clues.
Step 3: records
- Suffolk: replacements since July 2019 are registered with SCDHS, and I/A systems are registered under Article 19. The Office of Wastewater Management (631-852-5700) can tell you what is on file.
- Nassau: ask the town, city or village building department for permits on file for the property.
- Any sale: New York's Property Condition Disclosure Statement asks the seller about the system type, age and last pumping.
What to do with the answer
- Cesspool: keep it pumped, know the signs of failure, and read what you can replace it with.
- Septic: follow the pumping table for your tank and household.
- I/A: keep the maintenance contract current; see owner duties.
- Not on sewer and thinking of upgrading: grants pay most of an I/A system in many cases.
Frequently asked questions
How do I find out if my house is on sewer in Suffolk County?
Look the address up on Suffolk County's Septic Improvement Program eligibility map, which shows whether the property is sewered or inside a proposed sewer district. A sewer district charge on your tax bill or a sewer bill is another sign. Our town pages show how much of each hamlet lies inside a sewer district.
Which Nassau County communities are not on public sewer?
The Nassau County Department of Health's district list marks these as not publicly sewered: Bayville, Brookville, Centre Island, Cove Neck, East Hills, East Norwich, Flower Hill (western part), Glen Head, Glenwood / Glenwood Landing, Great Neck Estates, Greenvale, Kings Point, Lattingtown, Laurel Hollow, Locust Valley, Manhasset, Matinecock, Mill Neck, Munsey Park, Muttontown, Old Brookville, Old Westbury, Oyster Bay Cove, Plandome, Plandome Heights, Plandome Manor, Roslyn Estates, Roslyn Harbor, Roslyn Heights, Sands Point, Sea Cliff, Split Rock, Upper Brookville. Individual streets can differ, so confirm with your town or village.
How can I tell a cesspool from a septic system?
A septic system has a tank before the leaching ring, so solids settle out before water leaves; a cesspool is a single buried chamber that receives raw waste and leaches it directly. An operator can tell when the covers are opened. In Suffolk, a house built before 1973 that hasn't had its system replaced is the most likely to still have a cesspool.
What does an I/A system look like from the yard?
Tank covers at grade, a control panel with an alarm, and air intake and vent piping, according to Suffolk County's homeowner sheet.
Sources
Each source was re-read on November 7, 2026. Program amounts and rules change; the agency page is the authority.
- Suffolk County: SIP property eligibility lookup
- Nassau County DOH: Public sewer districts by community
- Suffolk County: Septic Improvement Program FAQ (4/2026)
- Suffolk County DHS: What homeowners should know about I/A OWTS (5/5/2026)
- Suffolk County DHS: Changes to wastewater practices effective July 1, 2019
- Suffolk County DHS presentation, 11/19/2024 (hosted by the Town of Shelter Island)
- Suffolk County Sanitary Code, Article 19 (I/A OWTS management)
- NYS Department of State: Property Condition Disclosure Statement
- Suffolk County GIS Viewer map service (hamlets, villages, sewer districts, groundwater zones, flood zones, tax parcels)
Have a cesspool or septic question on Long Island?
Submit a request and we match it to an independent, licensed Suffolk or Nassau County operator who serves your address. The operator contacts you to confirm the work and the price.
Request Service →