| Description | Quantity |
| Scale forming but non corrosive | >2 |
| Slightly Scale forming and Corrosive | 0.5 - 2 |
| Balanced but pitting corrosive possible | 0.02 - 0.5 |
| Slightly corrosive but non scale forming | −0.5 - 0.02 |
| Serious corrosion | −0.5 to −2 |