Conductivity is a widely used, general measure of water quality. While natural conditions (e.g., underlying geology and temperature) affect conductivity levels, changes in conductivity can indicate water pollution and higher conductivity values generally associated with poorer water quality.
How is it measured?
Conductivity is measured as the electric current that passes between electrodes placed in water. Water with more ions in it conducts more electricity, resulting in higher values. This can be measured in the field or lab and is corrected for the influence of temperature on conductance (i.e., specific conductivity).
Threshold levels
Because rivers and streams have a natural background conductivity level, which is strongly influenced by underlying geology, scoring thresholds vary depending on the ecoregion from which the sample was taken.
| Score | Piedmont ecogregions thresholds (µsiemens cm-1) | Ridges ecoregion thresholds (µsiemens cm-1) | Valleys ecoregion thresholds (µsiemens cm-1) | Coastal Plain ecoregion thresholds (µsiemens cm-1) |
|---|---|---|---|---|
| 5 | ≤42 | ≤21 | ≤49 | ≤56 |
| 4 | >42 – ≤100 | >21 – ≤66 | >49 – ≤137 | >56 – ≤108 |
| 3 | >100 – ≤158 | >66 – ≤130 | >137 – ≤267 | >108 – ≤182 |
| 2 | >158 – ≤249 | >130 – ≤214 | >267 – ≤430 | >182 – ≤257 |
| 1 | >249 – ≤544 | >214 – ≤521 | >430 – ≤626 | >257 – ≤526 |