Bob Noel wrote:

Would that water be contaminated if the shutoff to the water heater
had been closed (assuming it exists)?

Standard plumbing practice is to install a shutoff valve on the inlet to the
water heater to allow it to be drained. There is usually none on the outlet
line; security there would depend on the integrity of the various faucets in the
house.

George Patterson
Give a person a fish and you feed him for a day; teach a person to
use the Internet and he won't bother you for weeks.