Wet rising mains consist of vertical pipes similar to the dry rising main system with landing valves at each floor except the ground. The pipe system is connected to a permanent water supply, normally a tank fed from the town's mains. Duplicate automatic pumps, one duty and one standby supply water to the pipe system.
The tanks are fitted with an automatic warning system to indicate low water level.
At protracted incidents the wet rising main tank may need to be augmented and this can be achieved using conventional fire appliances and additional water supplies (hydrant, open water etc).
Wet rising mains are designed to supply 1500 litres per minute for 45 minutes as a minimum.
Due to the height of the building and the pressures used, water pressure reduction valves are fitted to the outlets at each floor. Buildings constructed prior to 2006 will have outlet pressures of 4 to 5 Bars. Changes to BS 9990 in 2006 now recommend an outlet pressure of 8 Bars, this recommendation does not affect installations installed before this date.