In an earthquake, you should be ready for no water for 3 days. In that case, it is good to have a hot water tank, rather than a smoggy in-line heater.
We got a taste of that at the old manor yesterday. We've been plagued by water main pressure drops all summer, but this was a doozy! The driveway down the road was lifted by a watermain break. Note to the wise - if you have a shitty old water main under your driveway, do not go for expensive patterned concrete!
Naturally, our professional screaming neighbours all screamed at the city. First the city said 3 hours, then more screaming, and they said 1 hour. What's it off their nose? They're off in an hour! The trucks all came and then sat there for 4 hours! We didn't have water from 5 pm to midnight. Then in the morning, all the water was mud! I'm still flushing everything!
If this happens to you, don't forget to flush out the hot water tank a few times over the next week, and turn up the temperature, if you have it too low. The soil is a wonderful source of Legionella!