Here in the US we have hot water tanks that store 30 - 75 gallons. Not sure I would drink it without filtering though.... You can also fill up the bathtub if you know beforehand....
You can get nasties like legionella growing in tanks if the temperature is hot but not hot enough to kill them. The insides of these tanks can be filled with oxidised metal bits too.
People underestimate water needs. Enough to drink, wash, brush your teeth, flush a loo unless you're digging a pit at the bottom of the garden to go in
If you’re cut off from civilization, you can probably prioritize a bit and only use water for the essentials. Which means no washing/showering or flushing the toilet for a few days.
