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Artesian Wells Explained

What "artesian" actually means, why some artesian wells flow on their own and others don't, and why an uncontrolled flowing well can waste water and damage the land around it.

What Makes a Well "Artesian"

The word "artesian" describes a specific hydrogeologic condition, not a type of water quality. According to the U.S. Geological Survey (USGS), artesian water is groundwater that is under enough underground pressure to rise on its own, sometimes all the way to the surface. Chemically and physically, USGS notes, artesian groundwater is no different from any other groundwater. The difference is entirely in how it reaches the well.

That pressure comes from a confined aquifer. USGS describes this as groundwater trapped between layers of poorly permeable rock, such as clay or shale, so that the water is squeezed under pressure rather than sitting freely at whatever level gravity would otherwise put it. The National Ground Water Association (NGWA) uses similar language: groundwater "separated from atmospheric pressure by relatively impermeable material" is called confined groundwater, and when a well penetrates that zone, water rises above the point where it was first struck because the aquifer is under pressure exceeding atmospheric pressure.

The Michigan Department of Environmental Quality's (DEQ) Flowing Well Handbook lays out the mechanics in more everyday terms. An artesian aquifer sits under an "aquiclude," an overlying layer with low hydraulic conductivity, or sometimes a slightly permeable "aquitard" that still transmits some water vertically. A recharge area at a higher elevation than the well loads the aquifer with hydraulic head, and the weight of the confining material adds more pressure on top of that. When a well casing punches through the confining layer and reaches the aquifer, that stored pressure is released and water rises in the casing, seeking equilibrium with the water level back at the recharge area.

Engineers and hydrogeologists track this using what's called the potentiometric surface: an imaginary surface, as NGWA defines it, to which water from an artesian aquifer would rise in a pipe. Whether a given well flows at the surface or just rises partway up the casing comes down to where that potentiometric surface sits relative to ground level.

Flowing Wells vs. Non-Flowing (Sub-Artesian) Wells

Every artesian well shares the same basic trait: water rises above the top of the aquifer it taps because the aquifer is confined and under pressure. What varies is how far it rises. Per the Michigan DEQ handbook, "in artesian wells, water rises within the well to a point above the top of the aquifer. If the water also rises above the ground surface, the well is called a 'flowing well,' or 'flowing artesian well.'" The handbook is direct about the relationship between the two: all flowing wells are artesian, but not all artesian wells flow.

USGS frames the same distinction around the potentiometric surface. When the level to which water would rise in a tightly cased well stays below the land surface, the well is artesian but non-flowing, sometimes called sub-artesian: water rises well above the aquifer, and a pump is still needed to lift it the rest of the way to the surface, but there's less lift required than in an unconfined well. When the potentiometric surface sits above ground level at the wellhead, pressure alone pushes water out at the surface with no pump needed, and that's a flowing artesian well. NGWA notes that historically, in the early development of some artesian basins, the potentiometric surface stood above land surface and produced flowing wells; more commonly today, the potentiometric surface sits above the top of the aquifer but below the land surface, which is simply referred to as an artesian well rather than a flowing one.

Topography can also drive this outcome independent of geology. The Michigan DEQ handbook notes that in unconfined aquifers, flowing wells can occur where the well intake is deep enough to intercept a zone where the hydraulic head is higher than the land surface at that particular spot, meaning the well is flowing because of where it sits on the landscape, not solely because of the confining layer above it.

Where Artesian Conditions Are Found

Artesian conditions depend on local and regional geology, so they aren't evenly distributed, and it's worth being specific rather than assuming any given property sits over a confined aquifer. NGWA's technical overview of confined groundwater discusses several documented U.S. artesian systems: it describes "artesian basins of the Great Plains and Rocky Mountain regions" that have been heavily pumped for decades, notes that base flow in many streams of the Atlantic Coastal Plain comes from natural discharge out of artesian aquifers into springs and streams, and references a USGS study of the principal artesian aquifer in the Savannah, Georgia area, where groundwater seeps through confining beds into shallow sands or the Atlantic Ocean. NGWA also points to the southwestern coastal basins of California, where artesian groundwater in some cases discharges into the Pacific Ocean below sea level.

At the state level, Michigan is a well-documented example of a state with widespread flowing wells. The Michigan DEQ handbook cites early-1900s groundwater investigations that identified about 200 flowing well districts in Michigan's Lower Peninsula, and department well-record data showing that roughly 450 flowing wells, about 3 percent of all new wells, were drilled statewide between June 2001 and June 2002 alone. The handbook names specific Michigan towns where flowing wells are common enough to be local landmarks: West Branch, Rose City in Ogemaw County, Cedar in Leelanau County, Indian River in Cheboygan County, Onekama in Manistee County, Conway, Oden, and Alanson in Emmet County, Naubinway in Mackinaw County, and Rapid River in Delta County.

The takeaway isn't that any one region of the country "has" artesian wells and the rest doesn't. Confined aquifers exist in patches tied to specific geologic formations, and whether a given property will hit one is a question for a local licensed driller and state well records, not a general rule of thumb. See our state-by-state contractor directory to find a driller who works in your specific area and can speak to local aquifer conditions.

Why a Flowing Well Needs a Control Valve or Cap

A flowing well that isn't fitted with a valve doesn't just look dramatic, it runs to waste and can damage the property around it. The Michigan DEQ handbook estimates that if every flowing well drilled in Michigan in 2001 had been allowed to discharge freely with no volume reduction, about 28 million gallons of groundwater would have been released from artesian aquifers every day, and uncontrolled discharge from new flowing wells alone would have amounted to over 30,000 acre-feet of wasted groundwater annually.

That's why Michigan's well construction code (its Groundwater Quality Control Rules, R 325.1621(3)(c)) requires flowing wells to be "constructed, equipped, and operated to prevent unnecessary discharge of water." In practice, that usually means a valved wellhead fitting, sometimes called a pitless unit with a flowing well spool, that lets the owner shut the flow down to whatever is actually needed and seal it completely when it isn't in use. The handbook also documents Michigan's Flowing Well Damages Act, dating back to 1905, which treats an artesian well left to waste in an unreasonable manner as a nuisance and makes the owner liable for damage the wasted flow causes to neighboring wells.

Uncontrolled flow isn't just a water-waste problem, it can undermine the ground and structures nearby. The Michigan DEQ handbook records a 1989 case in Alger County where a runaway annular flow (water escaping around the outside of the casing rather than through it) during a household well installation eroded an area 8 feet around the wellhead that reached the home's foundation before it was stabilized with 150 yards of gravel and 400 sacks of cement. A separate 1980 blowout in Oceana County flooded a house's basement and undermined its foundation badly enough that the dwelling was eventually condemned. Both cases trace back to the same root cause the handbook flags throughout: flow that wasn't controlled or properly cased off at the point it reached the surface.

If you own or are buying a property with a flowing artesian well, that history is the practical argument for a properly installed, maintained control valve, not just a code checkbox. A well that's allowed to run freely wastes an aquifer that took a very long time to recharge (NGWA notes the water moving through a typical artesian sandstone does so slowly enough that it can be in transit for hundreds or thousands of years) and it can quietly erode the ground around its own casing until something gives.

What This Means If You're Drilling or Evaluating a Well

If a driller tells you a property sits over artesian conditions, ask directly whether the well is expected to flow at the surface or simply rise higher in the casing without reaching it (non-flowing/sub-artesian), since that changes what kind of wellhead equipment and permitting you'll need. If it's a flowing well, confirm a control valve and watertight cap are part of the installation, not an add-on for later, and ask what your state's well-construction agency requires for casing and discharge control in flowing-well areas specifically. See our guide to hiring a licensed well driller for the broader list of questions to ask before signing a contract, and our well drilling cost guide for how casing and equipment choices affect price.

Sources: USGS, Artesian Water and Artesian Wells; USGS, Water Q&A: Artesian Well Water; National Ground Water Association, Confined or Artesian Groundwater; Michigan Department of Environmental Quality, Flowing Well Handbook (2005).