If the lot you like has no water main or sewer line in the street, the house will need its own water supply and its own wastewater treatment: a private well and a septic system. Millions of US homes run this way. The EPA says more than 26 million homes, about one in five households, depend on septic systems, and around 15% of the population, over 43 million people, rely on private wells for drinking water.[1][2]
For a new build, a well and septic system replace the water and sewer tap fees you would pay in town, but they bring their own permits, tests, design work and uncertainty. The good news is that most of that uncertainty can be removed before you buy the land. This guide explains how.
Key takeaways
- A septic system needs soil that can absorb wastewater; a failed soil test can make a lot unbuildable or much more expensive.
- Make your land offer contingent on a passed soil or percolation test and a septic permit, and ask about well depths nearby.
- Well cost depends mostly on drilling depth, rock and water quality, which nobody can know for certain until the well is drilled.
- In town, the comparable cost is water and sewer fees, which averaged $6,260 in the NAHB 2024 survey.
When you need a well and septic system
Most new homes connect to public systems. In Census data for 2025, 91% of homes built for sale had a public sewer and 9% had an individual septic system.[3] The share is higher for custom homes on rural land, which is where most well-and-septic projects happen.
Check three things on any lot listing: whether a water main and sewer line run along the street, whether the house would be allowed or required to connect, and how far the nearest connection point is. Sometimes a sewer line exists but is far enough away that extending it costs more than a septic system. Your local utility or public works office can tell you. If the lot has neither, you are budgeting for a well and a septic system, and the steps below apply.
| Public water and sewer | Private well and septic | |
|---|---|---|
| Main upfront cost | Tap, connection and impact fees | Soil tests, design, permits, drilling and installation |
| Monthly cost | Water and sewer bills | Electricity for the well pump |
| Long-term upkeep | Handled by the utility | Septic inspections and pumping, pump and water-treatment repairs |
| Biggest unknown | Fee schedule (ask the utility) | Soil conditions and well depth |
How a septic system gets approved
Septic systems are regulated mainly at state and county level, usually by the county health department or an environmental agency. The exact names vary, but the sequence is similar almost everywhere:
- Soil evaluation or percolation (perc) test. A licensed evaluator digs test holes and checks how fast water soaks into the soil and how deep the seasonal water table and bedrock are. Do this before you close on the land.
- System design. A designer or engineer sizes the tank and the drainfield based on the soil results and the number of bedrooms, and places them on a site plan with the required setbacks from the house, the well, property lines and any streams.
- Permit. The health department reviews the design and issues a construction permit.
- Installation and inspection. A licensed installer puts in the tank and drainfield, and the inspector checks it before it is covered.
Timing matters here. In some places soil tests can only be done in certain seasons, because the evaluator needs to see the soil when the water table is high, and health departments can have waiting lists. Ask how long each step takes before you agree on a closing date for the land, and leave room in your schedule for a second test if the first holes come back marginal.
Why bedrooms matter
Septic systems are usually sized by the number of bedrooms, not square footage, because bedrooms predict how many people will live in the house. If you might add a bedroom later, ask whether the system can be sized for it now. Adding capacity after the fact is far more expensive.
What drives the cost of a septic system
Septic prices vary so widely by state and soil that a national average would mislead you. What you can do is understand the factors that move the price, so you can read a quote:
- Soil. Sandy or loamy soil that drains well allows a conventional gravity system with a tank and trenches. Tight clay, shallow rock or a high water table can force an alternative system, such as a mound, sand filter or aerobic treatment unit, which costs more to build and often more to maintain.
- House size. More bedrooms mean a bigger tank and a larger drainfield.
- Slope and layout. If the drainfield must sit uphill of the house, you need a pump chamber and pump.
- Lot size and setbacks. A small lot may only fit the drainfield in one place, which limits where the house and well can go.
- Local rules. Some areas require a reserve area for a future replacement drainfield, extra treatment near waterways, or an annual maintenance contract for alternative systems.
Get two or three installer quotes based on the approved design, so everyone is pricing the same system.
Drilling a well: permits, depth and water quality
Private wells are also permitted locally, often by the same health department, and are drilled by licensed well contractors. The well usually has to sit a set distance from the septic system, property lines and other hazards. Those setbacks vary by state, so the site plan should place the well and the drainfield together.
The main things that set the price of a well are:
- Depth. Drillers usually charge by the foot, so depth is the biggest variable. Ask the driller and the health department about well depths on neighboring lots; state well-log databases often record them.
- Geology. Drilling through hard rock is slower than through sand and gravel.
- Casing, pump and pressure tank. The pump size depends on depth and how much water the house needs.
- Water treatment. If tests show hardness, iron, bacteria or other contaminants, you may need filters, softeners or disinfection.
- Trenching and power. The line from the well to the house and the electrical supply to the pump.
Private well water is not regulated like public water supplies, so the owner is responsible for its quality. Have the water tested by a certified lab after drilling, and ask your local health department which tests they recommend for your area and how often to repeat them. Your lender may also ask for a water test before the loan closes.
Protecting yourself before you buy the lot
The well and septic system are where a cheap lot most often turns into an expensive one. Build these protections into your purchase:
- Make the offer contingent on a passed soil or perc test and, ideally, an approved septic permit or design.
- Ask the seller for any earlier soil tests, permits or well logs on the property.
- Ask the health department whether the lot has been evaluated before and whether there are known problem soils in the area.
- Check whether a public water or sewer extension is planned. You may be required to connect later, and pay for it.
- Get a site plan early that shows the house, driveway, well and drainfield, so you know they all fit.
Our guide to choosing a building lot lists the other surveys and checks to run, and hidden costs of building a house covers power, gas and other utility connections.
How to budget for well and septic
In the NAHB 2024 cost survey, the average new home paid $6,260 for water and sewer fees and inspections, 1.5% of construction cost.[4] That line assumes public utilities. If you are on well and septic, replace it in the calculator with your real figures: switch the Water & sewer fees, inspections line to a lump sum and enter the combined cost of the soil test, septic design, permits, septic installation, well drilling, pump and any water treatment.
Until you have quotes, carry a larger contingency. Septic costs are not final until the soil test is done, and well costs are not final until the well is drilled. Our guide to the hidden costs of building a house covers other site costs that often get missed on rural lots.
Remember the running costs too. A septic system needs periodic inspection and pumping, and a well pump and any treatment equipment will eventually need repair or replacement. Ask your installer for a maintenance schedule and add it to your yearly home budget.
Plug your house size, land price and quotes into the free calculator. It uses the same NAHB 2024 averages as this guide.
Frequently asked questions
What is a perc test?
A percolation or soil test checks how quickly water soaks into the ground and how deep the water table and bedrock are. It decides whether a lot can have a septic system and what kind.
Can I build on land that fails a perc test?
Sometimes. An alternative septic system such as a mound or treatment unit may be approved, but it usually costs more. In some cases the lot cannot get a septic permit at all, which is why the test should come before you buy.
How deep will my well need to be?
Nobody can say for certain until it is drilled. Ask local well drillers and check your state’s well-log records for depths on nearby properties.
Is well and septic cheaper than public water and sewer?
It depends on the lot. In town you pay tap and connection fees plus monthly bills; on well and septic you pay more upfront and for upkeep but no utility bills. Compare real quotes for your lot.
Sources
- US EPA: EPA Encourages Homeowners and Communities to Maintain Septic Systems (SepticSmart, archived release) Verified
- US EPA: Private Drinking Water Wells Verified
- US Census Bureau: Highlights of 2025 Characteristics of New Housing Verified
- NAHB: Cost of Constructing a Home 2024 Verified
Figures last checked October 18, 2026. National averages are a planning guide, not a quote. See our editorial policy and data sources.
