In California, a retired electrical engineer has revived an out-of-production sonar device that uses very low frequency, or VLF, radio waves to locate underground water, and, as recently as Feb. 15, he has been successful. Using improved software, he found water where others had failed.
Richard Varian, owner of Survey4Water, Willits, Calif., uses the WADI VLF-sonar device—developed over 25 years ago by ABEM, Sundbyberg, Sweden—to find water trapped in rock fractures and cavities.