You should store 1 gallon of drinking water per person per day you are preparing for. You can get away with half of this in an emergency situation, but if you’ll also be out doing strenuous activities I’d suggest going ahead with a full gallon. Don’t forget, pets need water, too: my rule of thumb is a half gallon for every 50 pounds but your mileage may vary. It may be best to record how many times you fill the water bowl in your house per day, and the capacity of it and go from there. (When you have that value, I’d multiply it by 1.5 to be safe).
Water is cheap, easy to store, and in an emergency can be the difference between life and death.
Personally, I like purified water using reverse osmosis. I’m not a fan of spring water but many people are.
You can buy water in cases of bottles, 1 gallon jugs, or 5 gallon jugs. You can also get NEW food-grade blue 55-gallon drums and store your water there.
I like a mixture of bottles and drums. Bottles allow for ease of access and ease of transport. They are also cheap enough. $50 should get you more than 12 cases of 45 16-ounce bottles (or 67.5 gallons). That’s over 2 months of water for one person, or around 4 months of water in a real SHTF scenario.
Purified water comes clean, free of bacteria and chemicals (check the bottler’s quality report) and other unwanted things. It can store for a long time just by keeping it out of light and heat. When storing your own water, you must take precautions to make sure it is pure enough to be shelf-stable. The best option is to make sure the water you’re storing is pure and free of bacteria going in. This means boiling, purifying, or otherwise treating the water before it ever goes into storage. Water purification tablets work well for this purpose, but make sure you always keep some on hand for emergencies. If there is ever growth of anything in your stored water, you should throw it out.
Don’t ration drinking water. If you’re thirsty, drink water. If you’re low on water, drink water then work to secure a new source of clean drinking water. Rationing food makes sense as the body can live much longer than it tells you it can without food, but dehydration happens suddenly and severely and can keep you from making further rational decisions.
When drinking water from an unknown or untrusted source, use a filter like a sawyer, purification tablets, or boil the water for a full minute prior to consumption. Boiling will kill bacteria, filtering will filter out things like heavy metals and do a decent job removing bacteria, distillation will do both.
Chlorination also works to make water safe to drink. Use only pure bleach, non scented, non anything. Use 1/8 teaspoon per gallon of water and let sit for 30 minutes. You’re looking for your water to have a slight odor of bleach. If not, it’s possible you miscalculated volume, or that something in your water is keeping the bleach from working. Retreat the water once more and if still no smell of bleach, find another source of water.