Hard water is one of the most common causes of early solar water heater failure. Scale deposits clog FPC pipes, pit enamel tank linings, and drastically reduce heating efficiency. Many regions worldwide — from the Middle East to parts of Europe, Africa, and Asia — have water TDS ranging from 300 to 2000 PPM.
Understanding water hardness
Water hardness is measured in PPM (parts per million) of dissolved calcium and magnesium. The WHO guideline for acceptable drinking water is under 500 PPM, but solar water heater manufacturers specify different limits for safe long-term operation:
| TDS Range | Classification | Recommended Kaldor System |
|---|---|---|
| 0–200 PPM | Soft water | Any model — including FPC and SS 304 Eco Deluxe |
| 200–500 PPM | Moderately hard | ETC Diamond Glassline or Prime Ceramic |
| 500–3000 PPM | Hard to very hard | ETC Diamond Glassline only |
| Above 3000 PPM | Extremely hard | Water treatment required before installation |
Why Diamond Glassline handles hard water
The key is the non-reactive glass surface. Unlike enamel (which is microscopically porous) or stainless steel (which can corrode in certain hard water chemistry), the porcelain glass lining heat-treated at 850°C creates an inert surface that calcium and magnesium scale cannot permanently bond to. Any deposits that form wash away without pitting or rusting.
Additionally, Kaldor ETC tubes keep water completely separate from the solar collector — water only contacts the storage tank, never the tubes themselves. This eliminates the primary scale-failure point of FPC systems in hard water.
Signs your system is experiencing hard water damage
- Reduced hot water temperature over time
- Discoloured or cloudy water from the outlet
- White or yellow scale visible around outlet points
- Unusual smells from stored water
How to check your water hardness
Digital TDS meters are widely available and cost under $10. Take readings at your mains inlet (morning, before usage) and from stored water. If your TDS is consistently above 200 PPM, choose the ETC Diamond Glassline model and avoid FPC systems entirely for your installation.
Unsure which system suits your water quality? We'll advise.
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