Water Purifier

Underdwellers don't collect water from the surface, at least not directly. The gain water that dribbles down through the water table or from underground lakes and streams. This fresh water is certainly fine to drink if necessary, but usually contains many heavy minerals and thus can be detrimental to a person's health over time.
Water Purifiers are tasked with separating the minerals and sediment from the warren's drinking water. This is no easy feat. Accomplishing this daily via magical means would significantly drain the Darkweaver of their power. Better to have a tool or system that the average Underdweller can use. The profession requires much patience and is often boring, especially when it comes to the storage process. Much of the job involves checking and replacing the filters, keeping the filtration system in good repair, and making sure the water level and mineral content remains constant.
In the mountains, Underdwellers have something of an easier time. They use an aqueduct system from further upstream to run water through various cloths and other filters to remove the minerals. The water empties into large steel tanks in a collection cave. At the bottom of the tank is a tap through which water is sent past one final filter and into buckets for individual use.
The job is far more difficult in warrens without a nearby underground stream. They set up webbing that collects moisture, which trickles down through the water table and along the walls. Some of these locations even require tapping of certain plants to steal water. The water drips down to a central point and through the same filters used in the aqueducts, after which the process is the same. This method is painstakingly slow and requires frequent checks.
In smaller warrens, residents are expected to go collect their own water. Larger warrens will often require Purifiers to deliver rations of water to individual households.