I am living in Delhi and as all Indians especially Delhites would know in most places the water is hard. My current geyser has been repaired around 5 times as it gets damaged by the hard water from the borewell supply. Which geyser would you suggest is the best for hard water in India and how much do you think the geyser would cost? My current geyser is only a year and a half old and as mentioned been repaired 5 times, how long will the geyser for hard water go for without it being repaired?
Hard water normally does not cause a problem with water heaters. Are you sure its not the sand that is getting deposited in the tank near the heating elements? I use underground water at home as well but I have a 5 different storage tanks on the 5th floor terrace, two one-thousand litre tanks where ground water goes and then on a lower level I have three more one-thousand litre tanks fitted with an industrial RO system which shuts down automatically when all three tanks are full. It is a little complicated but for laundry I use ground water without any treatment so I would imagine it is as hard as what you get or even worse. My ground water is 1200ppm and anywhere you go in Delhi NCR you won't get anything worse then that. I have a solar water heater set up for the water that goes into the washing machine. Solar water heater is the one with glass tubes which are sealed in a vacuum. I got that installed about 8-9 years ago and never had a problem. For other use its individual gyser for each bathroom on every floor so can't say how they would perform with hard water as they are fed with RO filtered water. If nothing else I would suggest getting a filter for sand particles that I am sure make its way into your water heater tank and cause trouble.
Get one with longest warranty so you would know that at least for 5 years you won't have to worry about repairs.