Do you know how much water you use/consume on a daily basis?
Part of knowing how much water you need to store is knowing how much you use/consume on a daily basis. But not just you, how much does your whole family use/consume?
Of course, during an emergency or disaster, you might be using more depending on the situation, but you might also be using less.
It’s recommended to store at least 1 gallon of water per person, per animal, per day. However, that 1 gallon has to account for everything; drinking, hygiene, cooking, garden, etc.
And of course, you might have other sources of water, like a rain water barrel that you’ll need to account for.