What Should Be The Ideal TDS Count In Reverse Osmosis Water Purification System To Make Water Drinkable?

TDS in water isn't one the the critical attributes that determine if a water is drinkable.  If the TDS is high it can be safe but many people think it is unpleasant (cosmetic attribute).     From the U.S. EPA website: 

National Secondary Drinking Water Regulations

  National Secondary Drinking Water Regulations (NSDWRs or secondary standards) are non-enforceable guidelines regulating contaminants that may cause cosmetic effects (such as skin or tooth discoloration) or aesthetic effects (such as taste, odor, or color) in drinking water. EPA recommends secondary standards to water systems but does not require systems to comply. However, states may choose to adopt them as enforceable standards. 

 
• National Secondary Drinking Water Regulations - The complete regulations regarding these contaminants available from the Code of Federal Regulations Web Site. 
• For more information, read Secondary Drinking Water Regulations: Guidance for Nuisance Chemicals.

 

List of National Secondary Drinking Water Regulations

          Contaminant        Aluminum        Chloride        Color        Copper        Corrosivity        Fluoride        Foaming Agents        Iron        Manganese        Odor        pH        Silver        Sulfate        Total Dissolved Solids        Zinc