For your emergency supply of water you only need a short term supply, then if needed you will go to other water sources and sanitise that water for drinking. Authorities suggest storing at least 1 gallon of clean water per person per day. Half is for drinking, the other half is for cooking and sanitation. Use your emergency water supply anytime water will touch you or your food. Even if your tap water isn’t fit to drink, it’s still fine for flushing the toilet. It is not good for bathing, brushing teeth, washing dishes, cooking or drinking — that’s what the emergency water supply is for.

Of course, a gallon a day per person (half to drink and half for other stuff) is just a starting point. If you are sick, nursing, have kids or elderly people living with you, you will need more water. Those who are ill, pregnant or nursing may need a gallon a day just to drink. In hot or humid weather, plan on drinking at least a gallon a day for everyone. Keep enough emergency supply of water to last at least 3 days, although your emergency supply of water may last longer or run out quicker depending on how you use it.

To conserve your emergency supply of water, use disposable cups, plates and utensils. You may also clean your hands using waterless hand sanitisers to conserve water. If you run low on water, you may use tap water trapped in your water heater tank and pipes, but only if your tap water was safe to drink before. Do not ration water. If you run short, drink what you need today and find more tomorrow. Don’t risk dehydration. Do not use water from the tank on your toilet (the upright part on the back of the toilet. I know you wouldn’t try to drink out of the bowl!). Don’t forget pets. When storing clean water, treat pets just like people: a gallon a day each for pet.

Safely Storing Emergency Supply of Water:

Keep your emergency supply of water safe. Follow these tips from the CDC for storing water:

Keep emergency supply of water in a cool, dark place in your home, each vehicle, and your workplace.
It’s best to use bottled water. Use water before the expiration or “use-by” date stamped on the container.
It’s possible to keep water in food-grade containers intended for water storage. Containers must be thoroughly washed, sanitized, and rinsed (see below). Only store clean, ready-to-drink water. Tap water will probably need to be purified. Ask public health authorities or your water provider whether tap water should be used and how to treat it.
Plastic soft drink containers can be used in a pinch. Clean and sanitize containers before they are used (see below).
Do not use milk or juice containers for storing water. Even if you try to thoroughly clean these plastic containers, leftover sugars and proteins provide a perfect place for bacteria to grow.