Hardness of water is 1800 - Should pre-purifier be installed and then water be let into purifier ?

Hi,

I wanted to buy a new water purifier and approached one of the company. The executive checked the water and said that the hardness of water is 1800 (I amd not sure of the measurment system). He suggested that we should have another pre-purifier that needs to be installed before inputting the water into water purifier. Need advise.