Today I changed my water heater. I had to remove the water to pull it out. Well there is a lot of water 40 to 50 gallons. I think more then 75% of the population will die of not having water and will not even think about there water heater. So remember that if there is a large SHTF that you may find water in many homes.
This is something to remember if you live in an apartment building, many will leave the building so there will be many water heaters full of water.