If you hunt, fish or backpack out west, having enough water is a serious issue. You'll be sucking dry air and will need to consume a lot of water. Years ago we'd throw a canteen in our backpack, then we progressed to water bottles. Another option was chlorine pills to purify water, which didn't taste so good. Then they came out with some bulky pumps. When we packed into our backcountry elk camps, we'd fill two deflatable 5-gallon jugs which would last for a few days or you could boil river water.
Now there are other water filtration systems available. As long as you're traveling in locales that have streams, these will provide clean water.
Aquamira Frontier Emergency Water Filter System.
It consists of two parts, a filter and straw. When carrying it, I tie the pipe and straw together with a rubber band. It's so small that it can fit into your shirt pocket. It's good for 30 gallons. Many times I'll drink straight out of the creek, but it's more comfortable to carry a cup to dip water out of the creek and then drink out of the cup. The straw uses a charcoal filter, so don't freak out when you first use it. The water comes through jet black. Spit out the first few mouthfuls and then the water will clear up.
Aquamira Sport Water Bottle and Filter. Just scoop water out of a creek or lake and safely drink. Good for 100 gallons. This BPA-free, 25 fl. oz. bottle features a built-in, CR-100 Capsule Water Filter to give you an effective and lightweight on-the-go water filtration system. Reduces waterborne chemicals and improves water taste. Treats up to 100 gallons of water (640 refills).
If Buying Other Brands...
There are other water filter brands on the market but so far the Aquamira has done it's job. If you buy a different brand, just make sure that they'll eliminate Giardia and Cryptosporidium, which are the two leading causes of waterborne illnesses.
Keep Track of Gallons Used
Since the filtration systems in these are only good up to a certain amount, you'll want to keep track of how many gallons of water you've drank.
Go for the Cleanest Water
There are things that you can do to extend the life of your bottle/straw. It's filtering debris, so the cleaner the water you dip, the longer the filter will last. Don't dip muddy water out of a stream. Reach out where the water is clear.