We have come to a case study at a site in Palanpur in Gujarat, India where the excessive hard water has resulted in the reduction of life of solar water heater.
In Flat Plate Collector based solar water heater installed at Palanpur, Air vent pipe is regularly blocked due to excessive hard water and it needs to be cleaned regularly for efficient functioning of solar water heater. This is the first case I have come across in my solar career of 12 years that scale formation is occurring inside the air vent of solar water heater.
Sites like this need to use water softener plants prior to cold water inlet of solar water heater so that durability of solar water heater is increased.
You can see the scale accumulated outside the galvanised iron nipple used for air vent in below picture.