The short version, and why it matters more on Long Island than almost anywhere else.
Short answer: A cesspool is a single buried chamber that lets liquid seep directly into the surrounding soil while solids settle at the bottom. A septic system separates that process into a watertight tank (where solids settle and liquids clarify) and a distribution or leach field that disperses the treated effluent. Both need periodic pumping, but septic systems generally treat wastewater more thoroughly before it reaches the ground.
A cesspool is essentially a covered pit, often lined with concrete rings or block, buried below the drain lines of a house. Wastewater flows in, solids sink to the bottom and slowly break down, and liquid effluent seeps out through the pit walls and floor directly into the surrounding soil. There's no separate treatment stage — the surrounding soil itself is doing most of the filtering.
Cesspools were the standard system on Long Island for decades and are still common in older homes, particularly in parts of Suffolk and Nassau County built before the 1970s.
A conventional septic system has two main parts: a septic tank and a leach field (also called a drainfield or distribution field). Wastewater enters the tank first, where solids settle to the bottom as sludge and lighter material (fats, oils, grease) floats to the top as scum. The relatively clear liquid in the middle — the effluent — flows out into a network of perforated pipes in the leach field, where it's dispersed and further filtered by the soil.
Because the tank is watertight and does the initial settling separately from the field, a septic system generally provides a more controlled treatment process than a single-chamber cesspool.
Long Island sits on a sole-source sand and gravel aquifer that supplies drinking water to the whole region, and there's no municipal sewer connection for most of Suffolk County and large parts of Nassau County. That means whatever leaves a home's wastewater system goes straight into the ground that eventually reaches the water table and, in coastal areas, local bays and harbors.
Because cesspools do less pre-treatment than a septic tank and leach field, and because nitrogen from wastewater has been linked to harmful algae blooms and degraded water quality in Long Island's bays, Suffolk County changed its Sanitary Code effective July 1, 2019 to stop new cesspools from being installed as replacements for failed systems — see our Suffolk County regulations page for the specifics. If you're not sure which type of system your home has, that's one of the first things a licensed operator will confirm during a system inspection.
You generally can't tell from the surface. Clues that suggest a cesspool: a single round or square cover instead of a rectangular tank lid plus a separate field, an older home (pre-1970s) with no record of septic work, or a certificate of occupancy that predates modern code requirements. The only reliable way to know is to have a licensed operator locate and inspect the system, or to check any records held by the county health department for your property.
Submit a request and a licensed Suffolk or Nassau County operator will follow up.
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