What is the ideal TDS level in drinking water from RO and how to increase the TDS level in the filter?

I have got RO installed at my home. The input water is from overhead water tank linked to 300 ft deep borewell.

TDS of water from the overhead tank is 380 and TDS of RO water is 15. Please advise the ideal TDS required for healthy water and how to increase TDS of RO water?