Updated 2026-10-23
How can you tell if groundwater will be fresh or salty before drilling a borehole?
No survey can certify water quality before drilling: only a lab test of water from the finished, pumped borehole does. Before drilling you can narrow the risk with quality data from nearby wells and a drilling plan that seals off saline layers. On two dolomite farms in South Africa where geologists expected only salty water, WaterLocation's wells gave fresh water: 86 and 260 m³ a day.
What you can learn before drilling
| Source | What it tells you | Limit |
|---|---|---|
| Quality tests of nearby and earlier wells | Salinity at those points and depths | Says little about other layers or other fractures |
| Hydrogeological maps and records | Where saline zones are known in the region | Coarse; not drawn for your plot |
| Electrical resistivity surveys | Conductive layers in the ground | Ambiguous: clay and salt water both conduct |
| Fracture survey (WaterLocation) | Drilling point, depth to the water-bearing zone, forecast yield, casing plan for saline layers where relevant | Water quality is still confirmed by a lab test after drilling |
Salty water nearby does not always mean salty water for you
Groundwater quality can differ between layers and between fractures a short distance apart. A salty hole may be drawing from a different zone than the one a new borehole would reach.
On two farms in South Africa (dolomite), geologists and local drillers said any water would be salty. Six earlier attempts had given five dry boreholes and one with very salty water. WaterLocation's wells found fresh water on both farms: at 14 m giving 86 m³ a day, and at 97 m giving 260 m³ a day.
How to keep a saline layer out of a fresh borehole
- Plan casing in advance. Where saline layers are expected, the drilling specification includes selective casing or packers so salt water from one layer does not mix into the well.
- Log every water strike. Note the depth of each strike and a quick field check of the water, so the casing plan can be adjusted to what the hole actually shows.
- Test after pumping, not at first strike. Take the lab sample after a pumping test, when the water represents what the well will deliver.
Before you drill several holes
Drilling a few test holes to see where the water is fresh is expensive and, in rock, often inconclusive. A better order: collect existing well data and quality tests, survey the site for water-bearing zones, drill one well to a specification with a casing plan, then test yield and quality. WaterLocation surveys are quoted per site; the discovery fee is paid only after a pumping test confirms the water. See also finding groundwater in the desert and borehole siting methods compared.
Sources
Questions
Can a resistivity survey tell fresh water from salt water?
It shows conductive zones in the ground, but clay and salt water both conduct electricity, so a result can be read either way. It needs to be checked against well data.
Will the water from a WaterLocation borehole be fresh?
Quality depends on the site and is confirmed by a lab test after drilling. In WaterLocation projects the water has typically been fresh, including on sites where nearby wells were salty.
What should the lab test include?
At least salinity, plus the parameters your local drinking-water or irrigation standard requires. Ask the lab which tests apply to your intended use.