If you're aiming at using a particular water source that is near to you, why not find out NOW what you are likely to be dealing with?

Contact your local water board and see if they have any test results on chemical contamination (it should be public info). Biological contamination can be taken care of with boiling, it's the other junk that's the danger. And 'the other junk' also includes water contaminants that come from natural soil.

If they don't have any test results, ask them why not? And ask them if they would consider doing some.

The last resort would be to have the testing done yourself, which could be expensive. But don't just take a jar of river water to a testing facility and ask for a basic test -- all you get for your $10 or so is usually a fecal coliform test.

Sue