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....
Why would the hot water tank be more dangerous then the cold tap?
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.