Finding reliable groundwater in rural Southeast Asia has traditionally meant drilling blind — expensive, uncertain, and often unsuccessful. Electrical Resistivity Tomography (ERT) has changed that. Here’s how we use it.
ERT passes small electrical currents through the ground using an array of electrodes laid out on the surface. By measuring how electrical resistivity varies with depth and distance, we produce a 2D or 3D image of the subsurface — like a geological X-ray.
Water-saturated soils and rock have lower electrical resistivity than dry material. Clay layers — which act as aquitards — have very low resistivity. Clean sand and gravel aquifers have distinctive resistivity signatures depending on their water content and salinity. By mapping these patterns, we can identify where aquifers exist, how deep they are, and whether they likely contain fresh water.
In Preah Vihear Province, previous drilling had consistently failed to find productive water at depths below 30m. Our ERT survey identified a zone of low-resistivity fractured granite at 45–60m depth along a previously unexplored structure. A borehole drilled at the geophysically-defined target found a productive aquifer — providing sustainable water supply for the community where previous investigations had failed.
ERT is not a replacement for a well — it is what makes your well succeed. Used before drilling, it typically reduces overall investigation costs and dramatically improves success rates.
