How Deep Is a Water Well?
The median household well in the US is 142 feet deep, according to a 2021 US Geological Survey study. Dug wells are about 10 to 30 feet deep and driven wells 30 to 50 (EPA), while drilled wells may be several hundred to more than a thousand feet deep (USGS).
There is no single right depth. The Minnesota Department of Health says the depth of a well is decided by the depth to groundwater, the groundwater quality and the geology at the site, and that wells in Minnesota alone range from 15 feet to over 1,000 feet.
The table gives published depths by well type and for a few states. We found no government or university source for the 100 to 500 feet average often quoted online.
Water well depth by type and place
| Well type or place | Published depth | Source |
|---|---|---|
| Dug or bored well | About 10 to 30 feet | US EPA |
| Driven well | About 30 to 50 feet | US EPA |
| Driven well | Hand-driven around 30 feet; machine-driven 50 feet or more | National Ground Water Association |
| Drilled well | Several hundred to more than a thousand feet | US Geological Survey |
| All US household wells | Median 142 feet | US Geological Survey, 2021 study |
| Bored or shallow well | Generally about 100 feet or less | Water Systems Council |
| Drilled well in rock | Average about 250 feet | Water Systems Council |
| Minnesota | 15 feet to over 1,000 feet | Minnesota Department of Health |
| Maine, drilled wells | Average about 250 feet | Maine Geological Survey |
| California household wells | In the range of hundreds of feet | California State Water Board |
The same USGS study put the median public-supply well at 202 feet.
What decides how deep a well has to go?
Geology, mostly. The US Geological Survey says that getting an adequate household supply, usually 5 gallons per minute, depends on the permeability of the rock. Where permeable material is near the surface a shallow well may be adequate; where clay sits directly on bedrock, a deep well extending into the bedrock may be needed.
Neighbors are a rough guide. The Minnesota Department of Health says wells drilled very near each other often have similar depths, but that in glacial deposits the depth can vary greatly, even next door.
The Water Systems Council describes how it plays out on the day: a well contractor estimates from the average depth in your area, and if the first water tapped is adequate for your family, drilling can stop. If not, drilling may have to go deeper.
Is a deeper well better?
Deeper wells are less exposed to what happens at the surface. The EPA says drilled wells have a lower risk of contamination because of their depth and continuous casing, while driven wells can be contaminated easily because they draw from aquifers near the surface. The Minnesota Department of Health says dug, bored and drive-point wells are often less than 50 feet deep and are more likely to be contaminated by surface water, septic systems or chemical spills.
Depth alone is no guarantee. Penn State Extension says wells deeper than 100 feet can still be contaminated by coliform bacteria if they are improperly constructed. California's State Water Board says water quality may vary depending on depth and aquifer material, and Minnesota's health department notes that for arsenic, a deeper or a shallower well may solve the problem.
Deeper also costs more. The Water Systems Council says depth is a determining factor in the cost of drilling and pipe because most drillers charge by the foot.
Minimum depths in state well codes
State codes set a minimum for the casing, the pipe that lines the top of the well, not a target depth for the well itself. Three examples:
- Minnesota: casing must extend at least 15 feet below the ground surface (Minnesota Department of Health, citing Minnesota Rules chapter 4725).
- New York: casing must run from one foot above finished grade to 19 feet below it, with exceptions for local geology (10 NYCRR Appendix 5-B).
- Virginia: private wells must be cased to at least 20, 50 or 100 feet, depending on the well class (12VAC5-630-410).
How to find out how deep your well is
Look for the well log, also called a water well record or drilling report. The Water Systems Council says to ask your well contractor or state environmental agency for a copy if you don't have one.
The US Geological Survey says your state government probably maintains a database of drillers' logs. Minnesota's Well Index, for example, lists each well's location, depth, geology, construction and static water level.
Some states tag the well itself. Idaho's water department says a well's tag number is printed on a metal plate, about 2 by 3 inches, welded or riveted to the casing above ground; the number leads to the well's records.
Frequently Asked Questions
How deep is the average water well?
A 2021 US Geological Survey study put the median depth of household wells at 142 feet. The Water Systems Council says wells drilled into rock average about 250 feet, the same figure the Maine Geological Survey gives for drilled wells in Maine. We found no government or university source for the 100 to 500 feet range often quoted.
How deep should a well be for drinking water?
No agency gives one depth. The Minnesota Department of Health says depth is decided by the depth to groundwater, the groundwater quality and the geology at the site. State codes set minimum casing depths, such as 15 feet in Minnesota and 19 feet below grade in New York, and the EPA says deeper drilled wells with continuous casing have a lower risk of contamination.
Are shallow wells more likely to be contaminated?
Yes. The Minnesota Department of Health says dug, bored and drive-point wells, often less than 50 feet deep, are more likely to be contaminated by surface water, sewage from septic systems or chemical spills. The EPA says wells less than 50 feet deep are likely to be contaminated after a flood, even with no apparent damage.
Does a deeper well cost more to drill?
Yes. The Water Systems Council says the depth of a well is a determining factor in the cost of drilling and pipe, because most drillers charge by the foot. Our well drilling cost calculator estimates a total from depth and location.
How do I find out how deep my well is?
Check the well log, also called a water well record or drilling report. The Water Systems Council says your well contractor or state environmental agency can provide a copy, and the US Geological Survey says most states keep a database of drillers' logs.
General information, not a diagnosis of your system. Figures last checked against the sources below on 2026-11-13.
Sources
- US EPA: Learn About Private Water Wells
- US Geological Survey: Depth of groundwater used for drinking-water supplies in the United States (Scientific Investigations Report 2021-5069)
- US Geological Survey: Domestic (Private) Supply Wells
- US Geological Survey: Groundwater Wells
- US Geological Survey: How can I find the depth to the water table in a specific location?
- Wellowner.org (NGWA): Types of Wells
- Water Systems Council: Well Owner's Manual (2015)
- Minnesota Department of Health: Well Owner's Handbook
- Minnesota Department of Health: Minnesota Well Index
- Maine Geological Survey: Water Resources in Maine
- California State Water Resources Control Board: A Guide for Private Domestic Well Owners (June 2025)
- Penn State Extension: Coliform Bacteria
- US EPA: What to Do After the Flood (816-F-05-021)
- New York State: 10 NYCRR Appendix 5-B, Standards for Water Wells
- Virginia Administrative Code: 12VAC5-630-410, Construction; general (private well regulations)
- Idaho Department of Water Resources: Well Construction and Drilling
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