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Wells are holes in the ground that are filled with groundwater, which is pumped to the surface for us to use in our homes. There are both private and public wells located throughout Massachusetts with private wells used in many homes. 

MassDEP defines private wells as: “(they) provide water for human consumption and consist of a system that has less than 15 service connections and either (1) serves less than 25 individuals or (2) serves an average of 25 or more individuals daily for less than 60 days (about 2 months) of the year.” -




There are two types of wells: dug/bored wells and drilled wells. Dug/bored wells are holes in the ground dug by shovels or backhoes. Dug wells are particularly vulnerable to contamination because they get their water from shallow aquifers, where numerous toxins are concentrated.  In contrast, drilled wells go thousands of feet deep. They have a lower risk of contamination due to their depth and continuous casing. 

As an example, the Town of Stow does not have a centralized water delivery system; instead, residents and businesses completely rely on groundwater supplied from both public and private wells. Aquifer recharge and well depth both affect the vulnerability of each home's water supply.

Stow's wells could potentially be contaminated, depending on their depth. It is difficult to get comprehensive information on private well quantity and quality, but 

The other major threat to Stow's water supply is lack of the local infrastructure necessary to provide residents with water during extreme situations like droughts. When wells have dried up, residents have had to use bottled water for household needs. 

Residents should test their well water to ensure they are free contaminants and have secure supply during dry times. 

From the Ground Up

When you take water from a well, water from the ground slowly starts to fill the well up again. The rate of refilling has to do with how much groundwater surrounds the well and the size of the soil. The smaller the space between the soil particles, the slower the water fills up, or "recharges" the well.

Water withdrawals from wells differ from other water sources because they are solely based on groundwater levels, rather than surface waters, like rivers or lakes. In times of drought, ground water levels can decrease as well, which can lead to residential water shortages.


Once well water is used inside the home, it is either piped to a treatment facility or funneled to an on-site septic tank before returning to the ecosystem.  

groundwater infographic from USGS

Who monitors wells?

While the EPA (Environmental Protection Agency) sets permits for public water supplier withdrawals, private wells do not have the same regulations. Private well owners are responsible for ensuring that their water is free of pollutants. Owners can ensure the safety of their wells by regularly testing and ensuring that the well complies with the local board of health. A Private Well Regulation has been developed to establish criteria for private well sitting, construction, water quality and quantity.

private well infographic from USGS

To ensure that your well is in compliance with your local board of health's regulations, it is important for you to regularly test your well.  

Check out the EPA Guidelines for well testing to learn more about the testing process. 

For more information and/or any questions about wells, well testing, maintenance, or issues, click see FAQ to learn more. 

Effects on Water Cycle

water cycle infographic from  Effects on Water Cycle Santa Rose Plain Groundwater Sustainable Agency

A substantial portion of rainfall is absorbed by the ground. Rainwater that is not utilized by plants passes through pores and gaps in rock until it reaches a dense layer of rock. This water is groundwater and is a well’s water supply.  

Excessive water withdrawal can cause a “cone of depression” in the water table. A cone of depression occurs when a high flow rate well is installed too close to another well, pulling the water table down so low that neighboring wells no longer have water. A well that over-pumps the water table can permanently drop the water table and cause surface elevation to lower.

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