The average home has a 40gal hot water tank. Apartments and mobile homes might have a 20gal. Large homes may have a 60 – 80gal hot water tank. There is water storage right there partner. Most homes also have an indoor bathroom with a toilet. In the storage tank on the back of the toilette is another 3 – 5gals of water. No, not in the “bowl”, in the storage tank on the back.
The water is perfectly usable under normal conditions. Under emergency, disaster, or “grid-down” situations it may not be usable without filtration and purification. But that is OK, you have that capability as a prepper. Yes, anytime there is an emergency you should be filtering and purifying your water. You never know what might be wrong with it.
This is a “don’t panic” tip. You have more resources available to you than you think.