Sprinkler heads have to be heated to temperatures in excess of 60°C before they release any water. So in real life it is only the sprinkler heads that are nearest fire that will operate. As soon as water is discharged from the sprinkler head the area is cooled which prevents any other heads from operating.

What’s more, the amount of water discharged from a sprinkler head will be between 50 and 100 litres per minute, whereas a fire service hose will discharge between 1000 and 2000 litres per minute. So the water damage is far less with a sprinkler system that it would otherwise be. 

It is also worth noting that sprinklers are probably the most reliable fire safety system ever invented; with a false activation rate of less than 1 in 16 million per year.