Updated October 2026. Checked against U.S. EPA guidance.
A cesspool is an underground pit that lets untreated sewage soak straight into the soil. A septic system first holds wastewater in a watertight tank so solids settle out, then sends the liquid to a drainfield where the soil treats it. The EPA warns that untreated waste from cesspools can contaminate groundwater and drinking water, which is why some states now require cesspools to be replaced with septic systems.
Cesspool vs septic tank at a glance
| Cesspool | Septic system | |
|---|---|---|
| What it is | A pit or perforated chamber that receives raw sewage | A watertight tank plus a drainfield |
| Treatment | Little to none; waste seeps directly into the ground | Solids settle in the tank; soil in the drainfield treats the liquid |
| Groundwater risk | High, per the EPA | Low when sized and maintained correctly |
| Pumping | Frequent; the pit clogs as solids seal the soil | Every 3 to 5 years for most homes (EPA) |
| Legal status | Large-capacity cesspools banned federally since 2005; some states restrict or phase out others | Standard permitted system in all states |
What is a cesspool?
The EPA defines a cesspool as a shallow, underground system for disposing of sanitary waste. Older cesspools are often a pit lined with stone, block or perforated concrete rings. Wastewater from the house drains in, and the liquid leaks out through the sides and bottom. There is no separate tank to hold back solids, so the surrounding soil clogs over time and the cesspool has to be pumped or replaced.
How a septic system is different
A septic tank holds wastewater long enough for solids to sink and grease to float. Only the clearer middle layer flows out to the drainfield, where the soil filters and treats it before it reaches groundwater. That two-step design is the reason septic systems protect wells and groundwater much better than cesspools. For the full picture, see how a septic system works.
Are cesspools illegal?
Large-capacity cesspools are. Under EPA rules, all existing large-capacity cesspools, such as those serving multiple homes, apartments or businesses used by 20 or more people a day, had to be closed by April 5, 2005. The EPA notes that a cesspool serving only one single-family home is not covered by the federal ban, but state and local health departments may regulate or require replacement of it. Hawaii, which has many cesspools, has set a deadline to replace all of them by 2050.
If you are buying a home with a cesspool, ask the local health department whether it must be upgraded at sale and what that costs.
Have a cesspool or buying a home with one?
Replacing a cesspool with a septic system needs a site evaluation and permit. Talk to a local septic company about options and a quote.
Calls are answered by a pay-per-call partner network that connects you with a local septic company. Calling is free; we may be paid for referrals.
Replacing a cesspool with a septic system
- A site evaluation or soil test decides what system the lot can take: a conventional system, a mound or an aerobic unit.
- The old cesspool is pumped and then filled or removed according to local rules.
- Costs depend on the system type. The EPA puts repair or replacement of a conventional septic system at $5,000 to $15,000, and alternative systems can cost more.
- See septic system pros and cons and how big a septic tank you need.
Quick answers
Is a cesspool the same as a septic tank?
No. A septic tank is watertight and holds solids back; a cesspool lets raw sewage seep into the ground.
How does a cesspool work?
Sewage flows into a pit with porous walls. Liquid leaks into the surrounding soil and solids collect in the pit until it is pumped.
What is the difference between a cesspit and a cesspool?
The terms are often used loosely. In the UK, a cesspit usually means a sealed holding tank that must be emptied, while a cesspool in the U.S. usually means a leaching pit. Check how your local code defines them.
Sources
- U.S. EPA, Large-capacity cesspools (EPA archive, January 2025)
- U.S. EPA, Why maintain your septic system
- U.S. EPA, How to care for your septic system