I have a 40-gallons water heater, and I want to turn it to "vacation mode" because I will away be for 5 weeks. I am also shutting the water supply off, but obviously leaving house heating on - because I live in Toronto, Canada and it can get very cold in winter. Will water heater lose its water level from evaporation? And If I want to drain the house pipes as well to prevent any water flodding, will this affect proper functioning of the water heater?
Thanks for your advise

How could water evaporate if all faucets are closed?

If you are leaving your central heating ON I don't think you have to drain the entire house. Yes, you can leave heater on Vacation setting. That means, the pilot will stay ON entire time but thermostatic gas valve will be deactivated. Evaporation is not an issue at all...

I think it makes for a good practice to turn off water to the house when leaving for longer period. I always recommend it to my customers. I know from my own experience: it happened to me two times that when I returned from my trip my house was flooded. Once it was toilet supply line and second time it was washing machine supply hose.

Your heater will be fine on vacation mode, no watrer loss. You can generally set your home heat at 50 degrees and you will be safe. Lower than 50 may allow an isolated pipe to freeze if the temps get near zero outside. Alsobelow 50 the freezer section of some refrigerators will not function properly.

Thanks Milo Dolezal and ballengerb1 for your advise. Very much appreciated. I actually meant water loss when referring to evaporation. That`s clear now that I shouldn`t have any issues water left in the tank.
For the pipe draining, wouldn`t that add precaution on top of the water supply shutt off? Or am I overdoing it? Thanks again.

If you have concerns then drain the system butvif you leave heaqt on ir's not necessary. By all means shut the water off at the house shutoff when you leave. It's the cheapest insurance you'll ever get against flooding. Have a great vacation.
Tom
PS. Florida's great this time of year!