Hey All, I need some help. I've been doing alot of reading about back-flows. I guess it is very strict in the states. Here in Ontario I can't find any laws for installing back-flows, just that dual check valves "arn't code", and if the work is done by a contractor then a licensed plumber has to do the point of connection. All the companies around here just install dual check valves; but I read so many times that dual check valves are not for irrigation due to the fact that they can let toxins into the potable water source. My old boss, whose been in the industry for over 20 yrs (CIC CID CIT certifications) installs 3 systems a day on average. All of which are installed with dual check valves. Could it be that he has not read what I have? I'm planning on doing some of my own installs this year and I want to install proper back-flows. I have recently purchased a couple of Pressure Vacuum Back-flows and one double check back-flow. I was wondering, how well can PVB's withstand freezing temperatures? If the system is blown out correctly, is it safe to leave the PVB outside in the winter?