What is a good TDS level for RO? What is the Normal TDS Level of Drinking Water -50-150: Acceptable: TDS levels in the 50-150 range, on the other hand, are considered ideal. If you're using a RO water purifier, make sure the TDS level in the purified water isn't less than 80 mg/L. -150-250: Acceptable: In terms of cardiovascular fitness, this is the ideal TDS range.