Artesian well: what it is, and is its water safer to drink?

The short answer: an artesian well is a well that taps a confined aquifer, where groundwater is trapped under pressure beneath clay, shale or dense rock, so the water rises in the well above the top of the aquifer. If it rises above the ground, it is a flowing artesian well.

"Artesian" describes pressure. It says nothing about purity. A confining layer keeps surface water out better, but it does nothing about arsenic or radium in the rock, so test it like any well. Below: what makes a well artesian, what confinement does and does not protect against, state rules for flowing wells, and the tests to order. For wells in general, see how a private well works.

What is an artesian well?

The U.S. Geological Survey (USGS) gives the mechanism in its Water Science School page: groundwater "in aquifers between layers of poorly permeable rock, such as clay or shale, may be confined under pressure. If such a confined aquifer is tapped by a well, water will rise above the top of the aquifer and may even flow from the well onto the land surface."

USGS traces the name to "the town of Artois in France," where "the best known flowing artesian wells were drilled in the Middle Ages."

The level to which the water rises is the potentiometric surface (USGS also says "piezometric level"). The Minnesota Department of Natural Resources (DNR) gives the practical translation: it is "also described as the 'static water level' of a well completed in a confined aquifer." That number on your well record shows the aquifer's pressure.

The DNR's flowing wells fact sheet says drilling through the confining layer creates "a sort of 'pressure relief valve' which allows the water to rise above the top of the aquifer." Recharge happens elsewhere: USGS says the water "must seep down from the surface at a distance away and travel somewhat horizontally."

Flowing vs. non-flowing artesian wells

USGS draws the line at the wellhead: if the piezometric level is below the land surface, "the water will not shoot out of the well," and you still need a pump. If it is higher than the wellhead, the water "will be pushed upward in the well and emerge at the land surface, with no pump needed. This kind of well is a flowing artesian well."

The Minnesota DNR gives the range. Pressure "can range from slightly more than atmospheric to tens of pounds of pressure," and flows "can vary from less than one gallon per minute to hundreds of gallons per minute." Flow is not always constant either: "a well may flow only part of the year or in response to a number of variables such as atmospheric pressure or nearby wells being pumped."

Not every flowing well is artesian: the DNR says flow "can also occur in an unconfined aquifer," mostly near rivers and lakes.

Sources: USGS; Minnesota DNR.

Artesian well vs. drilled well: one is the aquifer, the other is the hole

"Drilled," "driven" and "dug" describe how the hole was made. "Artesian" describes the water it reached. The Minnesota DNR describes flowing wells as "drilled holes that encounter an aquifer with sufficient natural pressure," so an artesian well is normally a drilled well. A drilled well is artesian only if it reached a confined aquifer.

Depth does not settle it. USGS is blunt: deep wells "are often called artesian wells in ordinary conversation, but this is not necessarily a correct use of the term. Such deep wells may be just like ordinary, shallower wells; great depth alone does not automatically make them artesian wells."

So when a listing says "deep artesian well," read it as a sales phrase until the well log shows a confining layer above the aquifer and a static water level above the top of that aquifer. Our guide to finding well and septic records explains where to find the log.

What is artesian well water, and what "artesian" means on a bottle

For bottled water, "artesian" is a federal label with a definition. The FDA's bottled water standard, 21 CFR 165.110, says the name for "water from a well tapping a confined aquifer in which the water level stands at some height above the top of the aquifer is 'artesian water' or 'artesian well water.'"

The label does not require a flowing well: the rule adds that "artesian water may be collected with the assistance of external force to enhance the natural underground pressure." Nor does it describe quality. USGS, comparing artesian bottled water with spring water, says: "The water may not be different, but it comes to the earth's surface a bit differently."

Is artesian well water safer to drink?

Partly. Confinement can slow contamination soaking down from the surface. It does nothing about contaminants from the rock, and older confined water often carries more of those.

What a confining layer does protect against

A USGS study of New Jersey and Long Island aquifers (Water-Resources Investigations Report 99-4027) put it plainly: "Unconfined aquifers generally are much more vulnerable to contamination than confined aquifers." The report studied the surface-driven contaminants: nitrate, pesticides and volatile organic compounds.

The same sentence carries a condition: "For a well in a confined aquifer, the farther the well is from the unconfined area, the less vulnerable it is to contamination." A 2020 USGS-led study of Atlantic and Gulf Coastal Plain aquifers found that "primarily confined aquifers had young, oxic, low to near-neutral pH water near the outcrop (recharge area), and older, reduced, high pH water deeper and farther along flow paths."

How confinement gets bypassed

Wells are holes in the confining layer. A USGS fact sheet on the High Plains aquifer near York, Nebraska (Fact Sheet 2008-3025) traced young water in a confined-aquifer supply well to wells screened in both aquifers: "Multiscreened wells open to both aquifers offer conduits for downward movement of water (and associated contaminants) when the well is not in use."

The Minnesota DNR describes a 1950s flowing well at a roadside rest area that, a 2010 investigation found, "interconnected the overlying buried sand and gravel aquifers." Because of "the possibility for cross contamination," it was out of compliance, and the state "decided to seal the well."

An artesian well with a cracked casing, a poor grout seal or an old well nearby punched through the same clay is less protected than its geology suggests. That is why bacteria and nitrate stay on the test list, and why well-to-septic setback distances still apply to artesian wells.

What confinement does not protect against: the rock itself

Most of the health-relevant contaminants in private wells come from geology. USGS sampled domestic wells in principal aquifers for Circular 1332 (2009) and found at least one contaminant above a human-health benchmark in 23 percent of 1,389 wells. The most frequent were "radon, several trace elements (including arsenic and uranium), nitrate, and fluoride" (radon was compared with a proposed EPA level; there is no final federal radon standard for drinking water), and "except for nitrate, these contaminants in ground water all originate primarily from natural geologic sources."

Confined water tends to be old water, and time in contact with rock matters. In the Coastal Plain study (Degnan and others, 2020), USGS reported that groundwater was "more than 21,300 years old in more than half of 252 public-supply wells sampled," and that this "ancient groundwater is more likely to contain concentrations of fluoride, arsenic, and polonium-210 that exceed human-health benchmarks than is younger groundwater." The study measured untreated water from public-supply wells, not private wells.

The "sentry" threshold is half of a drinking-water benchmark: an early warning, not a violation. Above the full human-health benchmark, the study counted 0.8 percent of wells for fluoride, 2.4 percent for arsenic, 4 percent for lead-210 and 6.7 percent for polonium-210 (the journal article's figure; USGS's summary page gives 4.8 percent). Iron is the outlier in the chart: USGS found it "did not correlate with groundwater age."

The contaminants to know about in confined-aquifer water

Federal maximum contaminant levels (MCLs) apply to public water systems, not private wells; labs compare private-well results against them.

Arsenic

USGS Circular 1332 explains one route by which arsenic gets into water: "arsenic release from iron oxides, which is favored by low dissolved oxygen concentrations and high pH." Low oxygen and high pH are the conditions the Coastal Plain study found deeper along confined flow paths. USGS's brackish groundwater fact sheet adds that in brackish groundwater "arsenic can exceed the U.S. Environmental Protection Agency primary drinking-water standard of 10 micrograms per liter."

The Minnesota Department of Health (MDH) says "approximately 10 percent of private drinking water wells in Minnesota have arsenic levels higher than 10 µg/L," that "arsenic levels can vary between wells, even within a small area," and it "recommends that every well be tested for arsenic at least once." More: arsenic in well water.

Fluoride

A USGS national analysis of 38,105 wells (McMahon and others, 2020) found that the highest fluoride category "is associated with groundwater that has significantly greater pH values, TDS and alkalinity concentrations, and well depths, and lower Ca/Na ratios" than the lowest. In the Coastal Plain study, pH values likewise "increase with age." For domestic wells, McMahon found 2.6 percent above 2 mg/L (EPA's secondary standard) and 0.6 percent above 4 mg/L (EPA's MCL), and it notes that elevated fluoride is "regionally important, particularly in the western U.S." More on fluoride in well water.

Iron and manganese

USGS Circular 1332 says "relatively high concentrations of manganese coincided with low dissolved oxygen concentrations and low pH, because manganese-containing minerals are more soluble in water under these geochemical conditions." In the Coastal Plain study, iron passed the sentry threshold in 29 percent of wells. EPA lists iron and manganese as the tests for stained fixtures and laundry, and Circular 1332 notes that manganese "may have adverse neurological effects at high doses." See iron in well water and manganese.

Radium, uranium and radon

The clearest confined-aquifer case is radium in the upper Midwest's Cambrian-Ordovician aquifer. A USGS study released December 6, 2017 found that "water that was recharged into the aquifer long ago, that contains greater amounts of dissolved minerals, and that is low in dissolved oxygen is more likely to leach radium from its surrounding rock." Samples "from the confined parts" of the aquifer "frequently exceeded the USEPA maximum contaminant level of 5 picocuries per liter in Illinois, Iowa, and eastern Wisconsin, where wells tap deeper, older groundwater." USGS tested public-supply wells only and said the more than half a million private-well users on this aquifer "might consider having their water tested for radium."

Uranium and radon, both from the rock, are among Circular 1332's most frequent exceedances. They are separate tests. Our uranium and radium page explains gross alpha screening, and radon in well water covers the radon test.

Salt and dissolved solids

Deeper water is saltier on average. USGS's brackish groundwater fact sheet (2017) found that "about 70 percent of sampled wells between 1,500 and 3,000 ft below land surface produced brackish or highly saline groundwater; whereas, less than 20 percent of sampled wells between 0 and 50 ft below land surface" did. Median dissolved solids rose from 334 mg/L (0 to 50 ft) to 3,692 mg/L (1,500 to 3,000 ft). USGS defines brackish as 1,000 to 10,000 mg/L and notes that water above 1,000 mg/L "is generally considered undesirable for human consumption." EPA's secondary level, "a nonmandatory standard that only applies to public water systems," is 500 mg/L.

Under Florida Statutes section 373.203, one way a well becomes an "abandoned artesian well" is "discharging water containing greater than 500 milligrams per liter of chlorides into a drinking water aquifer." See salt, sodium, chloride and sulfate.

Flowing artesian wells: control, sealing and state rules

Why an uncontrolled flowing well is a problem

Per the Minnesota DNR, pressure "can cause water to flow above the ground level, sometimes with great force, causing damage to property and surface waters." Water can be forced "to flow around the outside of a casing that hasn't been grouted sufficiently," which "can cause erosion of the confining layer, erosion around the well, flooding, land subsidence, damage to structures, and safety concerns. This type of flow is difficult to control, and sometimes even impossible."

Some owners "choose to let the well flow so the water does not freeze," the DNR says, and flowing wells "may also waste enormous volumes" of groundwater. Its scale: "continual flow of just 1.9 gallons per minute will equal one million gallons of groundwater per year."

The DNR's extreme case: a 1995 cabin well in Aitkin County, Minnesota, flowed at "an estimated rate of 1,200 gallons per minute" and "shot up approximately 40 feet high." The contractor "worked for 20 continuous hours" with "an estimated 9,000 pounds of cement" to control it.

What the states require

Flowing-well rules are state law and differ widely. The four we read in full:

Sources: the statutes and rules named, plus the Minnesota DNR fact sheet. Other states have their own rules; ask your state well program.

Florida's section 373.207 also ordered each water management district to inventory "all known abandoned artesian wells" and plan their plugging; a well without "a properly functioning valve" counts as abandoned.

If you have a flowing well you can't shut off

Call your state well program and a licensed well contractor. The Minnesota DNR says higher pressures "can also make installing or sealing a flowing well difficult." Our old water well guide covers who may seal a well, and the fees, in the states it reviews. If water is coming up outside the casing, say so when you call.

Artesian wells and FHA loans

Buying a home with one? HUD Handbook 4000.1, Update 18 (issued August 12, 2026), says that if the property "is served by springs, lakes, rivers, sand-point wells, or artesian wells, the Property is not eligible for FHA mortgage insurance." Rules change; ask your lender. Our FHA, VA and USDA well water guide compares what each program says.

What to test in an artesian well

Start with EPA's baseline for any private well. EPA's private well page says to "test your private well annually for total coliform bacteria, nitrates, total dissolved solids, and pH levels," and to contact your local health department "to find out what substances may be common in your area's groundwater." Then add the geology-driven tests.

Not every well needs every line. Your state page and our tool for which tests to order narrow the list by location and situation. If your well is near a septic system, the septic system and well water guide explains which results point to it.

A worked example

Say your well log shows 70 feet of clay over a sandstone aquifer, casing set into the sandstone, and a static water level 15 feet below ground. The water rises above the top of the aquifer but not to the surface: a non-flowing artesian well. A first full test comes back with coliform absent, nitrate low and arsenic at 14 µg/L.

That result lands in the arsenic row above. It is above the 10 µg/L EPA standard for public water systems. MDH's guidance for that case: if tests "detect arsenic at levels above 10 µg/L, and repeat sampling confirms the results," it "recommends that you use an alternate source of drinking water or install a treatment system that reduces arsenic," and to let your medical provider know. The confining layer did its job on the nitrate. It did nothing about the arsenic. Our arsenic removal guide covers treatment options, and you can find a certified lab for arsenic to run the confirmation sample.

How to tell whether your well is artesian

Check the well log for three things:

1. A confining layer above the water-bearing zone: clay, shale or similar low-permeability material (MN DNR).
2. Where the casing ends: in the aquifer below that layer.
3. The static water level: if it is above the top of the aquifer, the well is artesian; if it is above the ground, it flows.

No log? Water that overflows the casing without a pump is a strong hint. Our well records guide lists where to search.

The bottom line for artesian well owners

Your artesian well may be better protected from the surface than a shallow well. But it draws old water, and USGS data tie that age to arsenic, fluoride, radium and salt. Test it like any well: the EPA baseline every year, the geology-driven tests at least once, and again after any change in taste, color or flow. Use our guide to how often to test well water for the schedule, and the lab finder to find a state-certified lab near you.

Questions people ask