Plumbing emergencies can and do happen at any time. In most cases the problem is a water leak and water being water it will find a way of escaping if possible!
All modern houses have a mains cold water feed from outside of the property. This feeds to a stop cock oops isolation valve inside the house usually in the cellar of an older terraced property or under the kitchen sink in newer properties.
What happens if things go wrong and what makes an emergency. Take an example of a problem we successfully dealt with not long ago. The cold mains feed was incoming to the house in a plastic pipe from the street. The householder wanted to turn the water off to do a bit of DIY on a tap washer and found that the isolation valve would not budge so he tried to close it using a pair of grips which through brute force twisted the brass valve fitting in such a way that it became separated from the feed pipe causing what you could quite reasonably call an emergency. Water at mains pressure literally erupted upwards hitting the shelf above in the sink base unit and sprayed a lot of water in a very short time all over the kitchen.
Within seconds the water was into and being soaked up by the hall carpet (carpets tend to shrink after such a soaking). Luckily one of our chaps was local and took the call. A quick look showed no sign of a water board valve out in the path but luckily our chap happened to have a 5 metre length of swimming pool plastic pipe with him. This was quickly fastened temporarily over the end of the incoming mains with the help of duct tape and hey presto the water is now flowing outside of the house. A call by us to the waterboard brought them along with some sort of a detector and a quick bit of digging by them exposed their valve which some kind soul had put tarmac over. A new valve in the house, re connect the incoming feed and all ok back to the DIY!