Ambiguities in TDS levels : Queries & concerns


From the discussions in the forums I have come to know that even very low TDS levels are not good for health. Hence I would like to know what is the minimum TDS level prescribed in the Standards. If there is no such minimum level then why it is not put into law if low TDS  hampers health. Also what is the TDS level of the bottled mineral water?   If TDS is to be maintained to 80-120 ppm  then which is the most cost-effective solution for domestic purposes?

Uttamkumar Bose