One of the many things that you will need in an emergency is water that will last you several days. You should stock up on water before it is too late and there is no more water on the shelf. People should not wait until there is a natural disaster coming to prepare for the disaster, or you may be left empty handed.
There are many good reasons to prepare for a natural disaster before the storm comes. The first reason is the roads may not be passable after a storm due to trees and live wires from electricity poles blocking the road. There could also be flooding, or other unsafe events which prevent you from traveling. It is better to have water on hand well in advance.
Another good reason to have water storage is, even if the roads are passable, the stores may not even be open after a storm if the store got flooded or lost electricity. The store counts on having electricity to run the cash registers. People can avoid being without water if they prepare for the storm before it happens.
Some of the ways that you will use water in a storm are: for drinking, for bathing, for doing the dishes, washing your hands, etc. You should have a good amount of water on hand for those daily activities.
You must ask yourself, if you went to the faucet right now, and no water came out, wow much water do you have stored for yourself and your family? Is it enough?