Water hardness is the concentration of calcium and magnesium salts in the water supply.
User manuals for new appliances sometimes recommend that you check water hardness levels in your water supply before connecting them.
The below table provides water hardness results during the 2019/20 financial year for the area previously serviced by Western Water. For more information please see the related Water Quality Report.
| Water district | Average hardness (mg/L) | Average German Hardness |
| Bulla | 17 | 1.0 |
| Darley | 83 | 4.6 |
| Diggers Rest | 15 | 0.8 |
| Eynesbury | 13 | 0.7 |
| Gisborne | 54 | 3.0 |
| Lancefield | 59 | 3.3 |
| Lerderderg | 80 | 4.5 |
| Macedon | 40 | 2.2 |
| Maddingley | 81 | 4.5 |
| Melton South | 12 | 0.7 |
| Merrimu | 87 | 4.9 |
| Mount Macedon | 41 | 2.3 |
| Myrniong | 115 | 6.4 |
| Riddells Creek | 37 | 2.1 |
| Rockbank | 11 | 0.6 |
| Romsey | 61 | 3.4 |
| Sunbury | 14 | 0.8 |
| Toolern Vale | 88 | 4.9 |
| Woodend | 29 | 1.6 |