Types of Well Systems:

Water Table Well Systems
The water table well is generally a more shallow type of water well. A water table well is drilled deep enough so as to penetrate ground water that has accumulated below the surface from rainwater that has percolated below. In New England, ground water table aquifers occur in formations in sand and gravel. This ground water is an normally excellent source of water as it has been filtered by natural formations.

Artesian Well Systems
An artesian well is generally a deeper type of water well drilled into rock or slate. When water is confined by a layer of overlapping impermeable formation such as rock or slate so that the water is under pressure greater  than atmospheric pressure, the water is said to be under artesian pressure.  In Massachusetts, the term artesian well is commonly called bedrock well. These types of well generally supply water of exceptionable quality.