In a tub you might get to see some Cherenkov radiation up close. Would be a nice silver lining to radiation exposure. :)

Ah. I actually thought filling the bathtub was a measure to mitigate the effects of the heat wave and maybe the radiation as well.

I think it's so if you survive, you have clean drinking water for when the infrastructure has failed and you're waiting for rescue.

This is exactly the thought. Water is the #1 survival necessity but an enormously fragile resource. Electricity can go out, pipes can burst, water supplies can be tainted. Some people keep years worth of canned food around but almost nobody has a year's supply of water.

Don't forget that the water heater has 50 gallons in it.

not in Japan. Japanese water heaters are on demand heaters. I love them becahse unlike US style tank based heaters Japanese on demand heaters never run out of hot water.

Ok but maybe it’s worth having a two stage system? In the event of the apocalypse..

Also a high school will have massive water heaters and a chiller..

Not in my apartment unit, it's one of those fancy in-line ones that let me run a shower long enough to rack up a hefty electricity bill.

Then I get poisoned because I didn't clean my bathtub as a often as I should.

Filling the tub provides you with drinking water and water to flush the toilet. It's standard practice in hawaii when a hurricane/tsunami is inbound.

Actually I read as to conserve water, predicting a possible water outage after infrastructure is taken out

This.

I live in Japan as well & told my family the same a long time back. There aren't that many other specifics you can plan for, with the family typically spread across the city on the average day, but at least grab a bathtub of clean water to see you through a few days till things settle down.