Water heater/tank: how to keep it when unused?

[yuli]

Some questions regarding slightly different technology, for those who have experience with keeping an electric water heater/tank system (several hundred liters capacity) in good shape during a period of prolonged non-use (a few weeks or longer) in this climate:
- should the heater be left switched on or can it be turned off?
- if the heater is left on, should some water be run periodically?
- if the heater is turned off, should the tank be drained?
Thanks in advance for suitable information!

[Ducked]

Not an expert, but I wouldn't have thought a few weeks would be a problem, assuming its sealed well enough to prevent it being a mosquito factory.

I'd have thought corrosion would, if anything, be slower if it isn't getting heated, and it presumably doesn't corrode very much in normal use.

Ultra-protection would be to drain and clean it, or add cathodic protection zincs, but I doubt either of these precautions is necessary.