Provided that the casing is still good, an old shallow well can often be brought back to life. Ongoing pumping, perhaps a pro clean-out using compressed air to blast out accumulated sediment, shock chlorination done properly, more pumping, and then regular testing.

I'm on a shallow well (about 40') but I have 39' of good, dense prairie clay, which is a first-class filtering medium. Testing for bacterial and drinking-water-chemistry standards looks fine. I really should have a few more layers, considering active farmland (herbicides) and oilfield (??) in the area.

The big worry is an entry point where biological or chemical contaminants can enter a clean aquifer. This is a "pioneer legacy" concern in my area, where old cribbed wells have been abandoned but not properly sealed. I think the same concerns would apply whey digging an improvised well. Know your onions.