"Dowsing is the action of a person called the dowser using a rod, stick or other device called a dowsing rod, dowsing stick, doodlebug (when used to locate oil) or divining rod to locate such things as underground water, hidden metal, buried treasure, oil, lost persons or golf balls, etc. Since dowsing is not based upon any known scientific or empirical laws or forces of nature, it should be considered a type of divination."
CrystalLinks.com

Vasse Water Divining focuses primarily on divining for water and occasionally minerals.

Here is a dowsing rod. It can be used for following streams after locating one.

Here is a Y-Rod. It is primarily used for locating a stream. The rod reacts with the minerals or water.