What is Water Hardness and Why Should You Care?
Water hardness measures the concentration of dissolved calcium and magnesium minerals in water. Hard water can cause scale buildup in pipes, water heaters, and appliances, reducing their efficiency and lifespan.
Understanding your water hardness helps you decide if treatment is necessary and what type of water softener to use.
How to Calculate Water Hardness
The formula converts calcium and magnesium concentrations to equivalent CaCO₃:
[\text{Hardness (ppm)} = (\text{Ca}^{2+} \times 2.497) + (\text{Mg}^{2+} \times 4.118)]
Where:
- Ca²⁺ is calcium concentration in mg/L
- Mg²⁺ is magnesium concentration in mg/L
- 2.497 and 4.118 are conversion factors to express as CaCO₃ equivalent
Unit Conversions
- ppm to gpg: Divide by 17.1
- ppm to mmol/L: Divide by 100.09
Calculation Example
A water sample contains 40 mg/L calcium and 15 mg/L magnesium.
[\text{Hardness} = (40 \times 2.497) + (15 \times 4.118)]
[\text{Hardness} = 99.88 + 61.77 = 161.65 \text{ ppm}]
This water is classified as "hard" and may benefit from softening.
Water Hardness Classification
| Classification | ppm as CaCO₃ | gpg |
|---|---|---|
| Soft | 0 - 60 | 0 - 3.5 |
| Moderately Hard | 61 - 120 | 3.5 - 7.0 |
| Hard | 121 - 180 | 7.0 - 10.5 |
| Very Hard | > 180 | > 10.5 |
Effects of Hard Water
- Scale buildup in pipes, water heaters, and appliances
- Reduced soap effectiveness requiring more detergent
- Spotting on dishes and glassware
- Dry skin and hair after bathing
- Reduced appliance efficiency and lifespan