The planned shutdown of hot water is carried out for the reason that equipment CHP and boiler needs maintenance. Boilers cleaned from scale, repairing worn-out equipment. It would seem that one or two weeks - a considerable period of time, but then the equipment runs smoothly, nearly a year. If such service was not made, equipment would fail unexpectedly, including on a winter's day that much more unpleasant.
In Western Europe many homes use a different system. Small boilers located in basements, and serve only the apartments of that house in which it is installed. Service this boiler is only one day a year, but from the point of view of efficiency it is much less efficient than large power plants.
Disconnect the cold water - a consequence of either an emergency situation or modernization of pipelines. The first happens more often. In most cases, accidents happen when abrupt changes in air temperature. They are eliminated quickly - sometimes water supply is resumed within the hour.
Sometimes the water in the riser entrance must be disabled because of the carelessness of one of the tenants. For example, if he went on a business trip, forgot to close the faucet, and the water flooded neighbors not to hack this door. If any of the tenants happens to be an accident in the heating system, have to disable it.
When upgrading the worn out pipes, including underground be replaced by other made of modern materials. Sometimes the old pipe is not removed, and a new stretch out within them. Replacement tubes are longer in comparison with the elimination of the accident, but then she is uninterrupted for decades.