Water is the most crucial thing to have in any survival situation. You can only survive three days without any water.
It is always best to have a water source with you as well as a means to purify water you find. I always keep a case of water bottles in my vehicle at all times in the event I may need it. If you are on foot, however, trying to carry a case of water is not very wise – a personal water hydration system that you can carry on your back like a backpack can carry 3 liters of water and is a much better option. Here are some ways to purify any water you might come across in a survival situation.
1. Boiling – Boiling is the safest and best way to purify water, but only if you have the means and time to make a fire. It might seem obvious now, but if you are already dehydrated and not thinking clearly, don’t forget to let it cool down before you take a drink.
2. Pumps/filters – (insert photo/link) Most stores with “outdoors” departments will have some sort of water filtration systems that will pump non-potable water through a purifier and straight into your water bottle. There are also some water bottles that have the filtration system built directly into them so that dirty water goes in and clean water comes out. You can also make a crude filter with some sort of cloth (t-shirt, sock, etc) packed with layers of grass, sand, gravel and/or crushed up ashes from your fire.
3. Tablets/drops – This is probably the easiest way to purify water on the go. Simply fill up your water bottle, drop in the specified amount of tablets/drops, and you are good to go. This method might leave the water a little bitter tasting (either from the iodine, chlorine, potassium permanganate, or other chemicals used), so bring along some gatorade or crystal light packets to mask the taste. Potassium permanganate will turn water to a light pink color for you to drink, and a darker purple color that you can use to treat some wounds and infections. Be careful with it though because it can cause a fire if mixed with certain chemicals. Click here to see how you can use that to your advantage.
4. Distillation/evaporation – These methods take the longest of all listed here, but could be your only option in certain circumstances. Distillation works especially well if you are surrounded by salt/brackish water, but it also requires the most equipment. You need a metal pot, tubing, a way to seal the pot with the tube in it, and a fire. As the salt water boils, the steam is cooled and forms water droplets on your tubing which drains into your water bottle. You can also tie a clear plastic bag around a bunch of leaves, and the sun will make the leaves “sweat,” filling your bag with water.
Remember, if you are feeling thirsty, your body is already 2% dehydrated. Drink water even when not thirsty or in cold climates. You can dehydrate in the cold just as well as in the heat. A very interesting, comprehensive guide with a LOT of great information about how to source, treat, and purify water for emergency use (especially in a 72 Hour Survival situation) that I read is called the Survive Water Crisis Survival Package if you would like to read further on this topic.