>> My flatmate claims that we should turn off this main pull switch after
>> using the shower, because when it's on electricity is always being used
>> to keep a reserve of hot water.
>>
>> I claim this is hokum and leaving the switch on is no different to
>> leaving the TV on standby.
>
> Indeed, you shouldn't leave the TV on standby, either.
OK, but my point is that leaving the TV on standby uses a negligible amount of energy - pennies a year probably. Isn't the same true of the shower pull switch?