Chemistry parameter
Electrical conductivity
How readily water conducts electricity, which is proportional to its dissolved ion content. Conductivity is the quantity a TDS meter actually measures.
Key facts
- Unit
- µS/cm
- Metric
- Electrical conductivity
What it measures
The concentration and mobility of dissolved ions. Uncharged dissolved substances, including sugars and most organic contaminants, contribute nothing.
How it is measured
By conductivity cell, conventionally reported normalised to 25 °C because conductivity rises roughly 2% per degree.
How to read a value
| Value (µS/cm) | What it indicates |
|---|---|
| Below 100 | Very low ionic content — rainwater, distilled water, soft upland surface water. |
| 100 – 500 | Typical soft to moderately hard public supply. |
| 500 – 1,500 | Hard groundwater supply. |
| Above 2,500 | Brackish influence. Seawater is around 50,000 µS/cm. |
Bands are conventional interpretation aids, not regulatory limits. Where a legal standard exists it is stated on the relevant standards page.
What causes it
- Dissolved minerals from geology
- Saline intrusion
- Wastewater and road salt inputs
Why it matters
- A sudden conductivity change is a fast, cheap early warning of a change in source or of contamination
- Ultrapure water for laboratory and semiconductor use is specified by resistivity — the inverse of conductivity — at 18.2 MΩ·cm
Related intelligence
Sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- National Institute of Standards and Technology — NIST Chemistry WebBook — thermophysical properties of water. Open · US Government work — public domain