To me this runs in the same realm of your neighbor's house/field/woods is on fire. Do you let the fire dept drain your pond to put out the fire? I would be in a very hard moral spot, but would allow the pond to be drained.

As usual I think a lot of this still falls in the realm of "it depends". In some areas an aquifier may be shared as there is an underground well-drained layer of porous material that water can travel through easily similar to an underground lake. Even if you are 2 miles from someone in this area you could realistically affect their water table fairly quickly as you would be draining this reservoir. In other places you have very poor flow, and the water sources are more localized, like where I live.

My house's water well is has very poor flow, and the well is over 250' to get it. Down the road a few hundred feet is a new house, and they recently drilled an artesian (sp?) well that has so much pressure the well cap sprayed water around it 10 feet out. They had to cap the well in an unusual fashion. Made me jealous as hell.

Summers like this I stress over my low water flow and it running dry, but my neighbors have to worry about cutting the lawn around their well head which still leaks. Apparently excellent water too. Makes me want to try dropping a well at the bottom of my hill to see what I get and see if I can hit the same resource. I would still have to pump up 200+ feet, but not straight up.