To keep from frostbite, the most important thing is to keep them dry, and you do that with ventilation. Which seems so counter-intuitive, we want to keep them warm, so we think we have to seal things up tight to keep that heat in.
Think of being in a car at night, with a bunch of people, unless there is a fan and a heater going, the inside of the car begins to condense moisture within minutes. And THAT is what you want to prevent in your chicken house. Lower your roosts a bit, so that they are not so close to the ceiling, leave the ventilation open, keep the droppings out on a regular basis and even when it gets down 20-30 below zero, they will be fine.
Cold and dry is not the same thing as coolish and wet. It is better to have no heat and be dry, than heat with moisture.
As for the water, use those black rubber bowls, and if you take them fresh water once a day, they will be fine.
Mrs K