Some Geiger counters can keep track of the cumulative dose for you, but most will simply display the rate at which you are getting exposed - typically in microsieverts per hour (µSv/h) or microroentgens per hour (µR/h; for gamma radiation, 1 R/h ≈ 1/100 Sv/h). To figure out what the reading means, you need to do the math: for example, at 600 µSv/h, you will hit 100 mSv within a week, and 1 Sv within about two months. (The usual background rate from natural sources hovers around 0.1-0.2 µSv/h.)
As for drinking untreated water: contrary to popular beliefs, in temperate climates, you are generally not taking huge risks by drinking from a backcountry lake or a creek; if it looks and smells all right, it's quite likely fine. On the flip side, a bout of diarrhea is probably the last thing you want to experience in such a situation, so it's good to take precautions if you can. Boiling your drinking water is a very robust method of eradicating microscopic wildlife (more about that soon). When boiling is not an option, adding several drops of regular, old-fashioned laundry bleach per gallon of water, then letting it sit for 30-60 minutes, will have a roughly comparable effect. Note that bleach has a limited shelf life; you will need to rotate it every 5 years or so. When on the go, sodium dichloroisocyanurate pills can be more convenient than liquid bleach and work just as well.

The Ultimate Survival Kit is the perfect upgrade for your survival needs.  Built to be durable under the most extreme conditions this bag will hold the contents of any of our survival kits as well as extra clothing and other personal items that you will need in an emergency situation.  There are 6 external pockets for easy access to your supplies.  The laptop compartment makes this a great daily commuter bag.  External straps allow you to strap on extra supplies and gear.