FEMA recommends storing water to last at least 3 days, with at least a gallon per person per day. In my opinion, that is not very much. People are supposed to drink at least 8 cups (1/2 gallon) of water each day. If it's hot, you're supposed to drink more than that. So, that only leaves 1/2 gallon for sanitation purposes; washing your hands being the most important. But what about flushing the toilet, taking a shower, and washing clothes and dishes. So, I would recommend storing 1 gallon per person for 2 weeks. Or more, if you have the space.
Several years ago, when I was 8 months pregnant with my first child, a water line broke in my community. I was at home, and needed to go to the bathroom (something that I needed to do frequently). But I wasn't too worried, because I was leaving in just a few minutes to go to the hospital for my Lamaze class. I would just go to the bathroom there. No! The water was off there, too! If you can only imagine a room of very pregnant women with no access to a toilet, or at least an operating one.
This is just one example of the importance of having as large of a water supply as possible.
How I store water:
1. I buy cases of bottled water when it is on sale. The primary reason for this is because it is convenient. If I'm on my way out the door, and I can't find my refillable water bottle, I just grab a bottle of water. And it gives me water storage.
2. I re-use empty juice and pop bottles. Yes, this is safe, because the bottles are food-grade. Do not use milk jugs, because the plastic will get brittle. Before storing water in your old juice and pop bottles, you need to clean and sanitize them. First wash with warm, soapy water. Rinse. Then fill the bottle up with tap water and 1 tablespoon of bleach per gallon. Most juice bottles are 1/2 gallon, so you would need 1/2 tablespoon of bleach. Shake well. Then, leave the bottle alone for 1 minute. Dump the bleach water out, and air dry. Then fill with water. I then write the date on the bottle with a permanent marker. I like to refill my bottles every 6 months, because water begins to taste funny after this time.
3. Keep water off the ground, in a clean, cool area. If you have extra space in your freezer, you can keep water jugs in there. Then it can serve a double purpose. If your power goes out, the fuller your freezer is, the longer the food will stay cold and safe to eat.
You can also store water in containers marketed for this purpose. There are plastic containers in all different sizes you can buy to store water in. If you purchase a 55 gallon water jug, you may consider putting it on a cart. This will make it more convenient to both fill and use.
Space saving idea: Connect bottles of water together with rope and hang from a closet ceiling on "S" hooks. Then, if you need to leave in a hurry, you can just sling them over your shoulder.