But it is you who control it. You know what you get and you take apropriate measures, if water quality is not good enough. Nobody will lie to you and your family that your water is good and certified for drinking. Also, it is a bad idea to live in place where so many pesticides, fertilizers,herbicides etc. around that they contaminate your well. It means that you have to leave that place as fast as possible. And water is not your main problem. As for usual well, drilled to correct layer, you will meet mostly with calcium salts, and may be iron ones. Both are not harmful, and could be easily conditioned to apropriate level.

Of course, there could be places where you could get water with natural heavy metals, or even radioactive ones, but in that case you got a jackpot. Your land become many times more expensive and yow you could choose any place anywhere, with best possible water for that money.