Division of Environmental and Community Health

Maine Center for Disease Control & Prevention

A Division of the Maine Department of Health and Human Services

DHHSMeCDCEnvironmental and Community HealthDrinking WaterDrinking Water ConsumersWell Types in Maine

Well Types


There are three types of wells commonly used in Maine: drilled bedrock wells, drilled overburden wells, and dug wells/springs. Of the three types, drilled bedrock wells are by far the most common source of drinking water for Maine homes.

Bedrock Wells

The typical bedrock well is six inches in diameter, one hundred to five hundred (or more) feet deep, and has a yield of less than 10 gallons per minute (GPM). Bedrock wells generally have steel casings, driven through the overburden, and 'set' into bedrock. A pump is placed in the well at a depth where sufficient quantities of water exist to handle anticipated use.

A couple of important points to make about bedrock wells:

  • Not all bedrock wells are 'artesian' wells. An artesian well is a particular type of well that is free flowing at the surface under natural conditions.
  • There is no water in bedrock. You can squeeze it all you want, but you'll never get water out of a rock.

So, if there is no water in bedrock, where does all the water in a bedrock well come from? It comes from cracks and fractures in the rock. When a well driller is drilling a well, he/she is searching for fractures that are full of water. Naturally, the bigger the fracture, the more water it can hold, but, just as important, the fractures have to be connected to some source of recharge – additional water that will refill the fractures as water is pumped out. The safe yield of a well is the rate at which water can be pumped out and at the same time be replenished by these sources of recharge. Keeping water use at or below the safe yield will ensure that your well will never run dry.

Following are some considerations a homeowner should be aware of when having a well drilled:

  • Is the driller licensed and in good standing with the proper regulatory agency?
    In Maine, well drillers and pump installers are licensed by the Maine Well Drillers Commission (207-287-5699).
  • Is the location you've chosen safe from potential sources of contamination? In particular, is it a safe distance away from any septic systems?
    The Drinking Water Program recommends at least 100 feet of horizontal separation between a private well and a private septic system(s), with greater setbacks for public wells and/or large septic systems. The well should also be as far as possible from oil and fuel storage, parking areas, sheds with equipment or chemicals inside, and agricultural fields (including home gardens).
  • Because of the above, the well should also be as far from property lines as possible. Your neighbor’s septic system or fuel tank can also contaminate your well.
  • Has the driller properly driven the casing into bedrock, and sealed it as required in your state?
    In Maine, a minimum of 10 feet of casing driven into bedrock is recommended.
  • Is there enough casing extending above the ground to ensure surface water will not enter the well?
    If surface water (rain runoff, snow melt, etc.) is allowed to pool on the ground around the wellhead, it may enter – and contaminate – the well and the drinking water.
  • Is the casing properly capped and any vents screened to prevent bugs and animals from getting into the well?
  • Has the well and water supply system in your home been properly disinfected?
  • Has the water from the well been tested for bacteria, nitrate & nitrite, arsenic, radon, and any other potential contaminant that may have entered from groundwater?

Long Term Care of a Bedrock Well

Know the limits of your well: don't allow it to be pumped dry. This is bad for you and your well, and especially the pump.

Do not allow contaminants to get into your well. This includes parking cars or refueling equipment near the wellhead. Never store or use dangerous chemicals near your well. Also, only apply fertilizers or pesticides as directed by the manufacturer, and if possible never apply them within 100 feet of your well. Your drinking water is much more important than a weed free lawn.

Keep all of the information your well driller gave you about the well, such as the depth drilled, the length of the casing, the location (depth) of any fractures encountered, and the safe yield. Be sure this information is kept in a safe place. It might come in handy in the future.


Artesian Well:  A well that is free-flowing at the ground surface due to natural pressure, usually a confined aquifer, which causes the water level in a well to be above the ground surface.

Bedrock:  The solid rock that underlies unconsolidated overburden materials.

Casing:  The 'pipe' used in well drilling to maintain a hole in the overburden. For most wells, the casing is 6 inches in diameter and made of steel.

Fracture:  Breaks in bedrock, some of which transmit usable quantities of water.

GPM:  Gallons-per-minute – The most common unit of measurement for describing the yield of a water supply well.

Overburden:  Unconsolidated materials such as clay, silt, sand, gravel, and boulders that overlie bedrock.

Recharge:  Water that originates as precipitation, infiltrates through overburden and then into fractures in bedrock, which is then available to replace groundwater removed by pumping.

Safe Yield:  The maximum amount of water that can be pumped safely from a well without risking damage to the well or the pump. The safe yield equals the amount of recharge.

Yield:  The amount of water being drawn from a well.

Updated 12/27/2022