Do I turn off my water heater if I turn off the water to the house?

We have a well that funishes 3 homes on our property. The other 2 are summer dwellings and are seldom used. Only now a nephew is using one of them a few times a week and there is a leak somewhere between the well and his dwelling. This is making the only pump we have turn on every 20 minutes. I would like to turn off the water to his place when he is not there. Do I have to turn off his water heater if I turn the water supply off to his home?

Your reply is greatly appreciated as it is a long walk to his dwelling and I'm not getting any younger.

Thanks,
Becky

recommended you should always turn off the power.will damage heating unit if it doesnt burn down the house first place.

Appreciate the input