Water in a water heater may or may not be potable. If the heater is kept below 140f, the water is not safe to drink. There's also a question of various soft met

Water in a water heater may or may not be potable. If the heater is kept below 140f, the water is not safe to drink. There's also a question of various soft metals in the tank itself as well as any connecting plumbing that may leech into the water. That's not a concern in a life or death situation, but you generally shouldn't drink hot water from your tap. All in all, you're probably better off with iodine tablets or some sort of filter.