The old water purification formula, as I knew it from my days of teaching survival:
Clear water2 drops chlorine bleach per quart of water
Murky water (sediments and assorted crud)4 to 6 drops of chlorine bleach per quart of water
Add chlorine drops to water. Shake to mix well. Loosen cap slightly to allow water to run over neck of canteen, so the neck gets purified too (after all, your lips will touch that neck when you drink). Allow to sit 30 minutes. Enjoy.
Remember that anything the water touches, that you put to your lips or eat from, must also be disinfected.
This purification method will only destroy live biological contaminants. It will NOT remove heavy metals, salt, alkaloids, petroleum products (diesel fuel, oil or gasoline), arsenic, etc.
Clear, apparently clean running steams and lakes are not indicators of purity. A rotten deer carcass just around the corner will introduce plenty of contaminants. Always purify; never assume.
Here in the remote Utah desert, I've seen springs both thick with green slime and crystal clear. Guess which one provides the best one for water? The one filled with green slime!
Think about it ... that green slime shows that it is not poisonous. But a clear spring almost certainly indicates the presence of arsenic, salt or alkaloids.
Arsenic is a common, natural element in many of the Western deserts of the U.S.
Chemical and petroleum pollutants are difficult to remove. Salts are nearly impossible to filter out with common means. Distillation may be the only methods, but it doesn't work with gasoline, diesel fuel or oil as they will evaporate before the water does, polluting your receptacle.
To remove petroleum products, add polluted water to a plastic beverage bottle. Allow to sit for a while. Petroleum products will rise to the top. Puncture the bottle at a point a couple inches above all sediment, but well below the level of petroleum. This is the water you'll drain off to be purified.
Water polluted with salt or arsenic can be evaporated, leaving the pollutants behind as the water turns to steam. Distillation can be done by boiling water in a kettle and suspending the lid at an angle just off to the side. Water droplets form under the lid, then run down and drop off the edge into a receptacle.
With the exception of using bleach, all of the above methods require time, effort and don't produce a great deal of potable water. However, it shows you what can be done.
The best method is to carry extra, potable water in your vehicle. A case of water bottles is better than one large container, as that large container may leak unnoticed. If one or two bottles leak, you'll still have plenty of water.
Be prepared. It's not just a Boy Scout motto, it's a way of life.
The grumpy ol' desert cat has spoken ...