Standing in the middle of a 400-acre ranch, Rob Thompson pulled out two L-shaped steel rods and held them perpendicular to the ground. … Thompson is a water witch who says he can find underground reservoirs and even pinpoint how far down to drill. … Water witching, also known as dowsing or divining, dates back to the Middle Ages. The American Society of Dowsers says it has about 2,000 members, many of them are working water witches. And while there is no science to back it up, it hasn’t stopped many of California’s top farmers and wineries from shelling out big bucks for their services.