Hydrants and risers are firefighting infrastructure rather than firefighting equipment: they exist so that the fire and rescue service can get water to a fire without running hose up a staircase. A building owner never uses them, and is entirely responsible for the ones on their premises still working when somebody else needs them.
Hydrants
A hydrant is a connection to the water main, usually below a hinged cover in the street or in a private road, marked with a yellow hydrant sign giving the size of the main and the distance to the hydrant. Crews connect a standpipe to it and take water from there. Private hydrants on a site are the site owner's to maintain, which includes keeping them accessible, keeping the marker plate visible and having them tested.
Dry risers
A dry riser is an empty pipe running up through a building with an inlet at ground level and landing valves on each floor. The fire service pumps water into the inlet and takes it out at the floor they need. It is used in buildings above a certain height where running hose from a pump would take too long. Everything about it is dormant until the day it is used, which is why it is tested.
Wet risers
A wet riser is permanently charged with water, fed by a pump and tank, and is used in taller buildings where a fire service pump could not deliver adequate pressure to the top. It carries all the maintenance obligations of a pumped water system: pumps, tanks, pressure, power supplies and the valves themselves, and it fails in ways a dry riser cannot.
What the owner has to do
Keep inlets and landing valves accessible and unobstructed, keep the cabinets closed and undamaged, arrange periodic testing including a wet test of the riser at intervals, and act on the results. Vandalised inlet cabinets and blocked hydrant covers are common and both waste minutes at the worst possible time. These are fire safety measures under the general duty to maintain like anything else.
Questions people ask about fire hydrant system
What is the difference between a dry riser and a wet riser?
A dry riser is an empty pipe the fire service pumps water into from ground level. A wet riser is permanently charged by its own pump and tank, used in taller buildings where a pump could not reach the top.
Who maintains a fire hydrant?
Public hydrants are maintained through the water undertaker and fire authority arrangements. Private hydrants on a site are the site owner's responsibility, including access, marker plates and testing.
Do building occupants ever use risers?
No. Risers and hydrants are firefighting infrastructure for the fire and rescue service. The occupier's duty is to keep them accessible, maintained and tested.