Shornhelm's substructure includes many interconnected cisterns, a honeycomb of pocketed caches which is connected to every potable well within the city. Many of them leak into each other as a consequence of age and shoddy craftsmanship, but only one distributes water on a grander scale! This cistern is referred to as the master source, as it allows flow from an underground river directly into every smaller cistern in the city. - To open the distribution channels you must first open both sluice gates, then turn the winch to start the external water flow.