Dowse for Water (sage ability)
Dowse for water is an amateur-status sage ability in the studies of Geology and Logistics, allowing discovery of underground water sources. While dowsing for water has a long reputation of being practiced though acts of superstition (in which a random chance allows enough occasional success to promote its mythology), the geological practice includes an understanding and insight into the surface of the Earth and its structure. There are various geologists who continue to employ the use of a 'dowsing rod,' insisting upon its usefulness — but unless the rod itself is actually a magically created wand, it serves no purpose where it comes to geologically identifying the location of water.
The ability is principally used for locating ground water so as to identify the best place to sink a well. The depth and usefulness of a well is important in terms of its cost in digging out, the time necessary to raise the water (deep wells take longer and can therefore service less people), the amount of silt in the water, its purity, the number of times it needs to be re-dug and its endurance in various seasons. It is notable that two wells as little as forty feet apart can have considerably different characteristics. Of course, the climatic or topographic region in which a well is dug will also change the success of finding groundwater and digging a valuable well.
Presume, for game purposes, that a character without sufficient knowledge in dowsing has a 3 in 20 chance of successfully locating a valuable well. These will typically have a a depth of 50-100 feet (d6+4 x 10), in land that is well-watered, but 1 in 4 useful wells will chance to have a depth of 10-40 feet.
Roll 3d4 +10 (x 10) to determine the depth that a poor well must be dug before reaching water in the same environment, with the understanding that any depth more than 150 feet must be considered worthless and too deep to dig further. Naturally, it will not be known if the well is worthless until that distance is actually dug.
The chance of successfully digging a well drops if the environment is not well-watered. Adjust the chance of finding water based upon the precipitation of the region, using an average monthly precipitation of 120 millimeters (4.8 inches) as a guide for well-watered areas. Thus, if the region has an average precipitation of 60 mm per month, the chances of an ordinary person locating a valuable well would be 3 in 40 (20 x 120/60).
Treat desert oases at 75% of well-watered for the purpose of this calculation.
If a character has an ability to dowse for water, however, then subtract 2 feet per knowledge point for all depth calculations. Thus, if a character had 11 points of knowledge in geology, the total depth of the well would be 22 feet less than the number obtained for any other person. Presume that minimum depth for a well would be 1 to 12 inches (roll the last foot with a d12) below ground level.
Note that even in deep desert, for a person with great skill in geology, there is at least some chance for locating near to the surface groundwater (excepting where actual rainfall is so low as to preclude the possibility) - it may only be necessary to dig a little. Presume that a landscape approximately a mile across can be dowsed for water (viewed and evaluated) over the course of one day.
