From InterceptRadio.com Wiki
Here are some quick tips regarding water storage.
Treat your water with regular (non-scented) Clorox which contains 5.25%-6% sodium hypochlorite.
Remember to use regular household chlorine based bleach. Do not use scented bleach or hydrogen peroxide based bleach.
For small quantities (like storing some water in your car) its best to use HDPE #2 plastic bottles. An example is filling a Nalgene 32oz bottle with 28oz of water plus 1 drop of Clorox bleach. The reason I don't fill car bottles to the top is to give expansion room in case of freezing.
For larger quantities its best to use HDPE #2 or PP #5 containers. An example is filling a 5-gallon bucket with water plus 1/4 teaspoon of Clorox bleach.
Using bleach in these ratios (1 drop per quart, 1/4 teaspoon per 5 gallons, or 2.75 tsp per 55 gallons) will result in about 3.2-3.5 ppm of chlorine in the water. Some agencies recommend double these amounts however I think 3-4ppm is plenty sufficient if you are using containers that have been sterilized with bleach prior to use. For comparison chlorinated tap water (and swimming pool water) usually has 1-3ppm of chlorine. The EPA limit for tap water is 4ppm. Once you hit 6-7ppm the water has a noticeable bleach taste to it.
Its best to only use HDPE #2 or PP #5 containers. Other containers can leach chemicals into the water. Do not use 2-liter soda bottles (PET #1) for long term water storage ! You can use 2-liter bottles for short term rotated storage (6 months) provided you keep the bottles out of sunlight. Another thing to note is you should never use plastic milk containers for water storage.
If you come across untreated water and want to purify it to be drinkable, follow these rules:
If the water is clear, use double the amounts of Clorox listed above.
If the water is cloudy, use quadruple the amounts of Clorox listed above.
If you have the means to do it, here is a better way to deal with untreated water:
Filter it (coffee filter, cheesecloth, paper towels, etc).
You can improve the filtering by cutting the bottom off a 2 liter bottle, putting cloth or a coffee filter over the neck from the inside, packing it with granulated campfire charcoal then putting about 2 inches of sand on top. Pour water over the sand and wait for it to drip out.
Boil it for 10 minutes
Cool it for 30 minutes
Add bleach (8 drops per 2 liter bottle) and wait 30 minutes
If it smells like chlorine then its drinkable, if not then add another 8 drops per 2 liters and wait 30 minutes.
If it still doesn't smell like chlorine then discard the water.
You can get some of the chlorine taste out of the water by swishing the water back and forth between two cups.
If you don't have any bleach you can distill the water by boiling it and catching the steam drops with a cup or a rag.
For filtering, figure on 30-80 microns for sand and 10-20 microns for a coffee filter.
A person should consume about 1 to 1.5 gallons of water per day and more if you are in a hot and dry climate. In any case, the liquid leaving your body should be at least 1/2 quart per day. If your breathing and heart rate are faster than normal its probably a sign that you are suffering dehydration.
If you are short on both food and water you should add 1/2 teaspoon of salt per quart of water to make up for electrolyte losses.
For extreme survival situations where you have a limited amount of water and want to use an absolute bare minimum amount, you can add 2 teaspoons of sugar per quart of water and drink about 1/2 quart per day. This isn't the healthiest way to do things but it should keep you alive.