Havells Monza EC 25-Litre Vertical Storage Water Heater (Geyser) is one of the best water heaters currently available on the market to deal with hard water TDS of more than 1200 ppm. This Havells Monza EC is specifically manufactured to deal with extremely hard water conditions.  Water becomes extremely hard when the percentage of total dissolved solids (TDS) reaches an insane level like 1200ppm. This kind of water is not only unsuitable as drinking water but also can damage water heater, water geyser, electric kettle, etc. Minerals like magnesium, and calcium are particularly responsible for making water hard. In this case, you need a water softener to make the hard water into soft water.