A mine adit is used to drain mine water from the mine by means of a channel in which the water flows by itself, i.e. by gravity only. In addition, like any other gallery, it is used for entry and exit, for transporting material and ore, and for ventilation. However, the main characteristic of an ore gallery is the continuous slope down to the mouth of the gallery.
The active pumping of water requires considerable expenditure, both on the necessary machinery and on obtaining the necessary energy. In the Middle Ages, physical labor, animals, and water power were used for this purpose, all of which required considerable effort. Of course, it was much more effective if the water ran out of the mine by itself. The disadvantage of such tunnels, however, is usually that they have to be built to the mine from a point as deep as possible in the surrounding area. This means mining long distances through waste rock, which means a large investment and has been a construction project for generations. Some adits in the Harz Mountains or Ore Mountains in Germany are several kilometers long and took a good century to complete. It was often only the grandchildren who benefited from the work. The owner of these tunnels had the right to collect a so-called draining fee from all mines whose water he diverted. The details were laid down in the mining law.
In addition to drainage, shorter mining tunnels also had the function of effective ore transport. Push cars with iron wheels on iron rails often had so little friction that they rolled out by themselves at the continuous low gradient. All that had to be done on the outside was to build a horizontal or even uphill braking track. In rare cases, there were adits through which the tubs drove themselves, or a miner rode along to brake. Usually the tub was pushed by one or two miners because the incline was not sufficient. In addition, there were often curves that could lead to derailment and had to be monitored.
And then there were tunnels through which so much water was drained that a channel in the middle or on the side was not enough. Such galleries were filled several decimeters high with running water. They were used only for drainage and ventilation, they were entered only for regular inspection tours. There are various show mines where such tunnels are entered by boats during the guided tour.
When a mine is abandoned and the pumps are turned off, the mine fills with groundwater. The lowest adit is the final level of the water filled part, because here the water is drained if the pumps are out. Levels above the adit are not filled with water. And in some cases the water dissolves parts of the ores, thus containing high amounts of certain substances. It is not unheard of that the water from the adit was collected and the minerals in the water deposited in huge pools. Today the potential hazard of a spring is much more important. Dissolved minerals in the water are generally considered pollution.