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Types of Water Wells Explained

Drilled, driven, and dug wells are built differently, reach different depths, and carry very different contamination risks. Here's how each type actually works, and which one you're most likely to find on a property today.

More than 43 million people, about 15 percent of the U.S. population, rely on a private domestic well for their drinking water, according to the U.S. Geological Survey (USGS). Those wells fall into three broad construction types: drilled, driven, and dug (sometimes called bored). The type matters because it drives two things homeowners care about most: how deep the well can reach, and how exposed it is to surface contamination.

Quick Comparison

Depth ranges above are from the U.S. Environmental Protection Agency's (EPA) private wells program. Actual depth on any given property depends on local geology and where the water table sits, so treat these as typical ranges, not guarantees.

Drilled Wells

Drilled wells are built with percussion (cable tool) or rotary drilling machines, per the EPA. USGS describes modern drilling as using truck-mounted rigs with rotary bits that grind through rock, percussion bits that pound through it, or auger bits where the ground is soft enough. Because the equipment can cut through rock, drilled wells can reach depths of several hundred feet and, per USGS, more than 1,000 feet in some cases.

Drilled wells require an installed casing, and in unconsolidated sediment (sand, gravel, silt) they also use a screen at the intake to keep sediment out while letting water in, according to USGS. In wells drilled into bedrock, the casing typically extends through the surface soil layer, with the well left open below that point. The National Ground Water Association's consumer site, Wellowner.org, adds that the space around the casing is normally sealed with neat cement or bentonite clay grout, which helps keep surface water and contaminants from tracking down alongside the casing into the aquifer.

Because drilled wells go deeper and use continuous casing plus grouting, the EPA states they have a lower risk of contamination than dug or driven wells. Drilling requires a specialized rig and a licensed operator, so it costs more up front than digging or driving a well, but it's the standard method for new residential wells today precisely because it can reach deeper, more protected aquifers. See our well drilling cost guide for what that typically runs.

Driven Wells

A driven well is built by driving a small-diameter pipe straight into soft, saturated ground, typically sand or gravel, according to both EPA and USGS. A screened well point is attached to the bottom of the pipe to filter out sediment as water is drawn up. Per Wellowner.org, driven wells put in by hand typically reach around 30 feet, while machine-driven installations can go somewhat deeper, to 50 feet or more; EPA gives a typical range of 30 to 50 feet.

Driven wells are cased continuously along the length of the pipe, but that casing is not sealed with grout, according to Wellowner.org. Because the well draws from a water-bearing layer close to the surface, EPA and USGS both note that driven wells remain vulnerable to contamination from nearby surface sources such as septic systems, fertilizer, or livestock, even though the pipe itself is intact.

Driven wells still show up today mainly for shallow, low-volume uses: things like irrigation points, temporary water supply, or older rural properties where a driven well was installed decades ago and is still in service. They're simpler and cheaper to install than a drilled well, but the shallow depth limits how much water they can reliably supply and how well-protected that water is.

Dug and Bored Wells

Dug wells are the oldest well type still in use, per USGS. Historically they were excavated by hand with a shovel down to below the water table, then lined with stone, brick, tile, or similar material to keep the sides from collapsing, and capped with wood, stone, or concrete, according to USGS. Bored wells are a mechanized version of the same idea, dug with an auger or backhoe rather than by hand. EPA lists a typical depth of 10 to 30 feet for this well type, the shallowest of the three.

Dug and bored wells have a large diameter and expose a wide area of the surrounding ground to the well, which lets them draw water even from less-permeable material like fine sand, silt, or clay, per USGS. That's a genuine advantage in ground where a narrow driven or drilled well would struggle. But because they aren't continuously cased or grouted, EPA and USGS both flag them as carrying the highest contamination risk of the three well types, and USGS notes they're also prone to running dry during drought since they can't reach much below the water table.

Dug wells are mostly historical at this point. Very few are installed new today; where they still exist, it's almost always because a well dug decades or generations ago is still standing on a property, not because anyone is choosing to dig a new one over drilling.

Why Depth and Casing Drive Contamination Risk

Across all three well types, the same two factors determine contamination vulnerability: how deep the well reaches, and how completely it's cased and sealed. Shallow wells sit closer to septic drain fields, animal waste, fertilizer, and other surface sources, and if the casing isn't continuous or grouted, contaminants have a more direct path down alongside the pipe into the water supply. Deeper, continuously cased, grouted wells put more soil and rock between the surface and the water being pumped, and the grout seal blocks that side-channel path.

That said, depth alone isn't a guarantee. USGS research on domestic wells nationally found that about one in five sampled wells contained at least one contaminant, most often naturally occurring metals, radionuclides, or nitrate, at a concentration above a human-health benchmark, regardless of well type. That's the reason EPA and most state and local health departments recommend testing any private well's water at least annually, and more often if you notice a change in taste, odor, or color, no matter how the well was built or how old it is.

Which Type Do You Have, and What to Do About It

If you're buying a property or troubleshooting a well you already own, well records held by your state or local health department can usually tell you how the well was constructed and how deep it goes. A visual check helps too: a wide-diameter well with a masonry or concrete lining is almost certainly dug or bored, a narrow pipe driven straight into the ground with no visible drilling equipment history suggests a driven well, and a well with a formal casing and grouted collar installed by a licensed contractor is most likely drilled.

If you have an older dug or driven well, it's worth asking a licensed contractor whether it can be deepened, or whether replacing it with a drilled well makes more sense given your water needs and the contamination risk at that depth. See our guide on how to hire a licensed well driller for what to check before any of that work starts, or browse contractors by state to find one near you.

Sources: US EPA, Learn About Private Water Wells; USGS, Groundwater Wells; USGS, Domestic (Private) Supply Wells; Wellowner.org (National Ground Water Association), Types of Wells.