I
Ian
I've never had one that's taken it any other way than as an accident. If you do happen to hit a pipe don't run round like a headless chicken, calmly turn the water off and open as many taps as you can to drain the water from the pipes. If its a gravity fed system uncover the hole in the pipe as quickly and calmly as you can and put your finger over the hole until the water has drained from the tank, or if there is someone with you get them to find the gate valve on the hot water cylinder or bung the feed from the cold tank with a parsnip (that's not a joke)
Do you carry a parsnip in the van, incase of emergencies?