Groundwater in most places usually isn't suitable for drinking, but used for things like golf courses.

It can depend on what kind of area you're in: farming country (agricultural chemicals) or city (fuel, antifreeze, garden chemicals, etc). One thing you might consider is to collect a jar of it and take it in to a local lab that tests water. Your local Cooperative Extension Office could probably help you with that, or check the phonebook. Water is always being tested for something, so someone will do it. Be sure to tell them EXACTLY what you want to know, or they may just charge you $8 and do a bacterial count, assuming its from a well. And this test won't tell you what's in the water three years from now when you need it, but it will guide you in the direction you need to go, and educate you in what you might be dealing with.

IronRaven's suggestion to filter (maybe a layered sand and charcoal filter) and then distilling it sounds good to me.

Sue