There is a federal website that has charts of the average water depth for most of the country...Where I live, it's about 8-10' on average. When I lived in El Paso, the city's wells were about 4000'. Now, it also depends on how porous the ground/soil is how deep you need to make the well so you can pump some out...you need the pump's depth far enough into the column so things can refill fast enough while you are pumping it out to meet your needs without the level reaching the pump as it won't do much pumping air! So, you may need to go much deeper than when you first hit water in say rock, versus going through sand where the water can flow back in with little resistance.
FWIW, there are ways to get a good estimate of how long the water has been underground...the water in El Paso averages about 10,000-years old and it's a losing battle...they do not get enough rainfall to recharge their aquifer, and the deeper they go, it tends to get saltier. They're pumping it out far faster than any is percolating down into the aquifer. The US desert SW and some of the west has a big problem with fresh water.
Where I live, there's lots of water, but we still may have some issues if it doesn't rain much.
Where I grew up, the town's spring fed water supply was like 1/4-mile from my home. If the power went out, our basement would fill up with about 6-8" of water fairly fast...the sump pump got a workout at least 1/2 of the year.
