Food may be important during a national disaster, emergency, etc, but what is more important than food in these situations is water. Some of the food you have stored away will probably need some water to cook it and then eat it. It is actually possible for water to be contaminated without someone noticing. The types of storage and where it is stored will cause such problems.
First, I will tell you what you should NOT use for storing water. The first is plastic that is non food grade. This type of plastic can leak a dangerous chemical into the water you put into it. They can also degrade after a while and some are really thin to where something like bugs, rodents, etc will be able to easily find their way inside a container. The second NOT to use is plastic that is food grade and has had previous things stored inside it that wasn't food. Any typd of chemical, which includes cleaner, could have soaked into it and has a possibility of soaking back out into your stored water. The third NOT to use is plastic that is food grade which had previously stored milk, syrup, juice, or fruit. The reasoning is because the sugars that are in milk and fruits are actually impossible to remove completely from the containers they were stored in, which can easily start a bacteria build up over a period of time. The fourth NOT to use is cardboard, since it easily breaks and can soak up materials that are unwanted, or leak. The fifth NOT to use would be anything else that is contaminated, other than stainless steel or glass since they both can be sterilized by putting them in boiling water for a minimum of 20 minutes.
There are plastics, however, that you can use. They are used by many due to the fact they are not as heavy as glass, a lot less likely of breaking, and is easily produced. If choosing to use plastic, food grade that is clean is the one to go with, and make sure to use an appropriate procedure for rotating the water. Like bottled water, it will need to be stored in an environment that is climate controlled without having sunlight exposure. Your best choice would be to use plastic tanks that are designed specifically for storing water, if affordable. They can come in barrel sized tanks that are able to hold 50+ gallons of water. The downfall of plastic tanks this size are they will be EXTREMELY difficult to move around. Therefore, if you needed to leave quickly, it would be more than likely you would have to leave them behind. Do not store the any of the containers or tanks close to any chemicals or fuels due to vapors from these can get inside plastic over a period of time. It is optional to use a wooden pallet to store large tanks or barrels on to avoid any spills touching them.
Another option is glass, which can be easily sterilized and does not have the same risks of chemicals being leeched into the water. The glass will also need to be food grade like plastic, since lead based crystal glass will leech the lead into the water eventually over some time. The main downfalls of using glass is that it can break very easily, it can be heavy, and has to be protected from the light. If your house, or wherever you store the water, is limited in storage space, it will have an advantage of being able to be stored close to chemicals like gasoline, etc because glass is impermeable. Make sure the glass you will be using is boiled in water for a minimum of 20 minutes and that it is completely dried before you use it. The best ways to lower the chances of the glass breaking are wrapping them in bubble wrap, paper, or foam. You could also put them inside of a cardboard box.
Stainless steel is a great alternative to plastic or glass. It is also impermeable and will not have harmful chemicals that glass has. The stainless steel is will be a lighter weight. It is also opaque instead of transparent like the glass is, so you will not have to be as concerned with storing it far from a light source. Sterilizing the steel will be easy and has a less likely chance of breaking. The main downfall of using stainless steel is you might need to have concern if the water you are storing has had a chlorine treatment since chlorine will be able to corrode the steel over a period of time. That problem can be solved, however, by acquiring a steel drum that is lined with protective coating. Always make sure they stainless steel you use for storing water is food grade
You might be wondering how much water you will need to store. Well, the average amount of water you will need is one gallon per person in your house per day. A half of that gallon is used to drink and the second half of the gallon will be for hygiene. There will be some factors that will change the amount of water needed. Living in a hotter climate or having a nursing or pregnant woman will require you to store some more water than the average needed. The amount of days you will prep for without having water will depend on how well prepared you will want to be for a variety of disasters. The normal amount of recommended water from FEMA to last in your household should be three days if water supply at your house has been disrupted. Those three days should get a household through the water shut down or contamination that could happen when a natural disaster happened like ice storms, tornadoes, or earthquakes. However, a more general consensus seems to say you should store enough water to have on hand for a minimum of two weeks. That will be 14 gallons of water for one person, so a household with five family members would need 70 gallons of water.
One of the most important responsibilities of storing water is rotation, will depends on where you are able to store the water. If plastic containers are being used, or if containers are stored in an area that is not somewhat temperature controlled, or light is exposed sometimes, the water needs to be rotated every six months, or not stored longer than six months. An ideal condition for storage, like a sterilized stainless steel drum that has clean water and stored inside an environment that is temperature controlled, you can store the water up to a total of three years before any rotation is needed. Do not use water being rotated out for consumption, or drinking water. When opening a container, it will need to be used in a short amount of time after it is opened. Drinking water in time from a drum that is 50 gallons will be quite difficult. I would use that water instead for cleaning and washing clothes, watering your plants, etc. This is known as "gray" water.
Once you get down the basics, you should be ready to store the amount of water needed for your family. Just remember the amount needed will depend on how many family members you have. Also remember to store the water in an ideal area, using the type of storage of your choice.