| Sign | Electrical conductivity (dS/m) | Description |
| So | <4 | Without salinity limitation |
| S1 | 4 - 8 | Low salinity limitation |
| S2 | 8 - 16 | Relatively high salinity limitation |
| S3 | 16 - 32 | High salinity limitation |
| S4 | >32 | Very high salinity limitation |