To build a Water Mine, learn water mining technology at a University of Thought that has unlocked it. You will need the following materials to construct a Water Mine:
The Water mine must be built near the edge of a body of water.
Water mines that are built too close together will interfere with each other. The minimum distance is about 20 coords. [In Tale 1, this distance was about 16 coord] (You will receive a notification if you are about to build one mine too close too another.)
A water mine is operated by winding the collar spring, which will cause it to run for 2 hours. The winding does not use an endurance timer, and statistics like strength or endurance seem to make no difference.
As the water mine runs, periodically it will sound a gurgle and a gem may appear in the tray. The gem can be retrieved from the tray, but if it is not retrieved within 1 minute it washes off the tray and is lost. The gurgle is audible for quite a bit farther than most building sounds (~50 coords?).
Pyramid of Many Wanders has doubled the gems produced
The water mine that has a pitch that can be set to a number from 10 to 30. The pitch affects the rate at which gems appear in the tray, and it is also believed that it may affect the types of gems that are produced. However the nature of the relationship is not understood (see Theories). Many players suggest trying a pitch for 5 to 10 minutes to see if gems are produced and switching to a new pitch if no gems appear.
The types of gems that appear are cuttable gems (Amethyst, Garnet, Lapis, and Turquoise) as well as the quartz, diamond, emerald, ruby, sapphires, and topaz (has no graphic on tray) that come from Ore Mines. Cuttable gems look like quartz when they appear on the tray.
There is an menu option to listen to the water mine, which usually will say that the "telltale tinkling of gems" is heard. This means that the operation of other water mines are not interfering with the one being checked.
In Tale 1, the operation of a water mine was found to lower groundwater levels in its vicinity, which can, among other consequences, affect the growing of certain vegetables near the water mine. In Tale 2, there is not yet an ecology skill that allows us to measure groundwater accurately, so this point is speculative. [ I have not been able to see any effect on veggies even with 4 watermines around a growing spot, so I think this was dropped for tale2 - Cappu ]
There is a public set of water mines (currently 4) run by Cappu near Karnak at 620,90)