Actually, the cistern and waterline are 8 ft. deep. I haven't yet had a problem with freezing. That's not to say it can't happen. It just hasn't happened yet.

Thanks. Sounds like an awesome setup.

Even though my waterline is 8 feet deep, it still has to come up through the frostline, into the house. At the bottom end of the waterline is where I reduced it from 3 inches to three quarter inch. The three quarter inch line comes up through a 3 inch standpipe. This way, if the line does freeze, I can slide a heat tape down there or use my wife's old blow dryer to circulate warm air down along the line. At least, that's the theory.