There are several types of drilled wells. I do not know all the different names, but the one that most people refer to is an artesian well which is a well that they drill looking for ledge and veins of water going through it. One very seldom locates ledge close to the surface. They have what they call a gravel packed well which is also drilled but doesn't need to go so deep. I have heard that these can collapse and needs to re-drilled to clear it. I have no idea why this is a good well but many people choice to have them. It may have something to do with cost. When one digs a sallow dug well they hope that they do not hit the ledge and/or large boulders and depend on the water coming usually from deeper in the ground and being forced up towards the surface. Most dug wells are feed from the bottom of the well and not the sides.
I am sure others will comment on this and correct me, but I'm just stating the information that has been passed onto me over the past 60 years.
