Need to know if a TDS level of 101 from RO system in Chennai, TN, is harmful - Will changing pre-filter solve the problem

Dear Sir

I am using Eureka Forbes RO system. My feed water TDS level is 685 ppm. After fiteration, TDS is reduced to 101 ppm.

The following link shows Rejection rate should be around 90-95 % i.e  TDS after filteration is around 70 ppm

Link: http://www.tdsmeter.com/what-is?id=0003

I have a baby less than a year old. Please advice TDS level of 101 ppm is harmful for domestic use ?

Does changing pre filter alone will result in TDS level reduction?

Thanks in advance for your advice

Thanks

Arun