[craigwblake]

> I thought there was some scientific method and Well Witchers/Dowsers had been relegated to history

Nowadays a professional hydrologist is who you'd contract for the task. They will do a geologic survey and fracture trace analysis using data from satellite imagery, the USGS and related state agencies in order to identify fissures within the underground rock formations that are most likely to hold a suitably sized pocket of water with good recovery. Then they might conduct electrical resistivity tomography to directly measure and image the density of subsurface material to identify water pockets and narrow down good drilling spots. It's a far cry from the sort of thing that might be characterized as dowsing.