Another thing occurred to me: occasionally, municipal water is contaminated. I read about towns having to require everyone to boil their water for some reason or other for a few days. If you have a few score gallons in your hot water reservoir, you'll need to clean that out.

The other issue is cross contamination from water and sewage mains. In our area, if we have an earthquake, the water pipes and sewage pipes are likely to be ruptured, resulting in contamination of the water supplies, even if you have some water pressure. You then have your couple hundred gallons with some raw sewage in the supply.

Everything's a compromise, so you get to make your analysis and use your judgment as it applies in your situation. Then you get to live with your decision.