Septic system or sewer? How to tell

Many homeowners don’t know whether their house is on septic or sewer, especially after buying a home or moving from the city. A few quick checks usually settle it in an afternoon.

Why it matters

A sewer sends your wastewater through pipes to a treatment plant run by a city, county or private utility, and you pay for it on a bill. A septic system treats it on your own lot with a tank and a drain field, and you are responsible for its care. NC State Extension notes that septic owners should budget for inspections and pumping instead of a monthly sewer bill.

If you have septic and don’t know it, the tank can go unpumped for years. That is how a cheap pumping turns into a drain field replacement.

Check 1: your water or utility bill

This is the fastest test.

The EPA’s septic FAQ lists a $0 wastewater charge, or no bill, as a sign of septic, and a private well with no water meter as another. Hawaii’s health department says it the other way around: a sewer bill or sewer charge means the property is served by a sewer. If the bill is unclear, call the utility and ask whether your address is connected.

Check 2: property records

The EPA suggests looking at your deed, building permit and house plans, which often show whether there is a septic system. Your home inspection report from the purchase may mention it too.

The best record is usually at your county or local health department, which issues septic permits. Many counties let you search online by address or parcel number. King County, Washington, for example, has site designs, inspection reports and as-built drawings that show where the tank and drain field are. Records can be missing for homes built before the early 1970s or for systems installed without a permit, so no record doesn’t prove there is no septic.

Check 3: look in the yard

If the records don’t settle it, look outside:

• Follow the main drain. Find where the main sewer pipe leaves the house (often in the basement or crawl space) and note which way it heads.
• Look for a lid or riser. The EPA says you may find a round access riser, often black or green, usually about 10 feet from the house.
• Look for a mound. Some drain fields are built into a small raised mound in the yard, according to the EPA.
• Watch the grass. A rectangle of lawn that stays greener, or a row of slightly sunken strips, can mark a drain field.

Grass and soil often cover the lid. A licensed septic company can find a buried tank with a probe or a locator.

Don’t pry open a lid you find, and never lean into or climb into a septic tank. The gases inside can kill a person very quickly. Leave opening the tank to a licensed septic company.

Check 4: ask around

• Neighbors. The EPA notes that if the houses around you have septic, yours probably does too.
• The city or county utility. They can say whether a sewer main runs on your street and whether your house is connected.
• The previous owner or the last service company. A company that pumped the tank before may have the size and location on an old service report.

If you have septic, what kind is it?

Most homes have a conventional system: a tank and a gravity drain field. Others have a mound, an aerobic treatment unit or another advanced design, as the EPA’s guide to types of septic systems describes. An air pump, an alarm panel or a control box in the yard usually means an advanced system, which needs more frequent professional service. The permit drawing tells you for sure. Our guide on how a septic system works explains the parts.

What to do once you know

If you’re on sewer, there is no tank to look after. Keep grease and wipes out of the drains and you’re set.

If you’re on septic:

1. Find out when the tank was last pumped. If nobody knows, book an inspection.
2. Find the tank size on the permit or a service report.
3. Set a schedule. Our guide on how often to pump your septic tank has intervals by tank size and household.
4. Mark the tank lid and drain field so nobody parks or builds on them.

Buying a home? Our guide to buying a house with septic covers what to ask for before closing.