I ran across this web site that explains the static electricity involved and why some are better at it. "Divining rods and all common dowsing devices, are the simplest forms of electroscopes. The bent rod for example is just a variation of Gilbert's straw needle electroscope. The divining rods are charged with static electricity from the dowser's own body. This static electricity can be seen quite adequately with a simple millivolt meter. This voltage is measured between the hands of the dowser, to measure this voltage accurately a diff amp should be used at the input to the voltmeter, "this eliminates stray signals which are common to both hands". The amount of voltage will vary depending on the person. A good dowser will have a high reading, "above 100 mv" while a poor dowser may read as low as,"0 mv.". For males the right hand is usually a negative polarity, and the left hand is positive in polarity. These polarities are usually reversed in females. The divining rod charged positively will rotate in the dowsers hand to line up parallel to a negatively charged object being dowsed. A divining rod charged negatively will remain perpendicular to a negatively charged object being dowsed. This is because like charges repel, while unlike charges attract. Thus both bent divining rods are not required for dowsing. When two divining rods are used, and they are seen to cross, one of the rods is being moved to line up parallel with the charged object being dowsed. The other rod is moving to line up parallel to the first rod. A second reason for the two rods crossing is that of dowsing over an alternating current source, such as a pipeline or buried cable. these are usually buried shallow and are conducting ground currents as the path of least resistance."
Scientific Evidence of Dowsing