Water is a high priority commodity during a time of disaster. There are things that you can do in your home immediately before a potential or impending disaster (e.g. hurricane, tornado), or right afterwards (e.g major earthquake) to ensure an emergency supply of water for drinking.
Note: I’ve done a number of posts on this over the years, but it’s a good reminder to realize where your water sources are, or what you can do to quickly store extra water for your home.Note: Shut off the utility water supply to your house if there’s reason to believe that the public water supply may have been contaminated.
Tool: Water & Gas Shutoff Valve

Fill your bathtub, sinks, and other available containers with water. You could potentially collect 50 to 100 gallons of water in a full bathtub – enough to water a family of four for several weeks. Consider a waterBOB for your tub…

Toilet Water. The water that’s in the toilet tank (not the bowl) is perfectly fine. You will find anywhere from 2.5 gallons or more setting there.

Drain your water heater for 40 gallons or more. Turn off the gas or the electric power to your water heater before draining. Open a hot water faucet somewhere in the house. Then, on the hot water heater there will be a drain valve/spigot located at the bottom of the tank… open it to allow water to drain out of the tank. Drain the tank into containers as needed. If there is some sediment in the water, just let it settle, and drink the water off the top.

Drain the pipes in your house. The piping in your home typically holds several gallons of water, which can be drained into containers by opening a high-point faucet tap and draining from a low-point tap.

Rain Water Harvesting. You might step outside and set up a tarp to collect rainwater into buckets or a barrel. An amazing amount of water could be collected in this manner:
Calculate Gallons Of Rainwater Collection From A Tarp
Note: Use a drinking water filter. When in doubt, filter it out…

Source:modernsurvivalblog.com