Dry-riser-iconThe pipes in sterile risers are empty and are just filled with water from firefighters when they arrive. Firefighters will connect the pump socket in one of the appliances into the dry riser inlet. Bs9990 Water is then drawn in the nearest public fire hydrant (fed by the water provider's service main) and this is pressurized by the fire pump to provide water at the right flow and pressure for fire fighting operations at the relevant floor amount.