Roof-mounted solar water heaters were very common in South India too. Our childhood home had two solar panels heating a tank of water. Worked very well in summer, and there was a backup electric heater for the winter months. We also got some rebate from the electricity supplier, if I remember correctly.

The entire system was quite simple, and hasn't needed any maintenance in close to 20 years, I think?

What are the benefits of solar electric panels compared to water heating panels?