Minimum TDS level for drinking water : Is it possible to set TDS levels on RO systems

Recently as a salesman was giving a demo on a RO system, he told that the TDS level will be reduced to 10. Is it a safe TDS level or all the minerals will be removed if it is very low. But i read somewhere that the ideal mineral water should have a TDS level atleast of 150. What should be the minimum TDS level for the drinking water and what should be the maximum? Will the RO systems allow us to set the required TDS level?? If so what should be the thumb rule used to set the same?