Water is more important than food to survival. It is also bulky and needs to be refreshed periodically. Water can be stored in special barrels . In a pinch, you can use whatever containers you have on hand. If you drink pop in 2 liter bottles, the empties build up quickly. The bottles also wash out pretty thoroughly (unlike milk jugs) so your stored water stays fresher. To store water, add about 6 drops of household bleach per gallon (unscented bleach only!). This water may not be tasty when you crack the seal, but it should stay drinkable for months.

Another option is to get a second hot water heater and plumb it in before your existing hot water heater. You don't need to turn it on. The purpose is to have an extra 40 gallons that is always fresh, since it is constantly replaced as you use water in your house.

If you store water in barrels or jugs, you'll need to make sure your stored water doesn't freeze or have a way to thaw it if it does, so you may need a way to move it into a heated area of the house. With barrels you'll want to keep a dolly handy. It's best though not to move barrels of water once filled. They are extremely heavy! Water weighs about 8.2 pounds per gallon.

Store extra bleach for sanitizing in general and purifying drinking water in particular. Other water purifiers, like iodine pills could be stored as well.

If you have an outside source of water, a good water filter will be more efficient than storing large quantities of bulky and heavy water. After a lot of research, I purchased an Aqua Rain filter. I chose this filter because it removed practically everything that I wanted out of my water, including 75% of the fluoride in tap water. Even the Berkey didn't do that (unless you bought a second filter add-on, which I didn't want to do). The Aqua Rain is a gravity filter, which allows the water to flow slowly through ceramic filter cartridges to remove the smallest particles. The cartridges can last for years and no electricity is required. It will even make pond water safe to drink.