THere are some disadvantages with open 'wells': things including animals (amd humans) can fall into and foul up the water in the well; not all/everywhere ground water is good (enough). in some places water can be salty or brackish, full of some undesirable minerals, and some can weels dry up in summer time just when we need water most.

But if you have a good well, it is worth looking after it, make sure no children fall into it and protect it ;-)