What is the reason for low TDS in RO purified water how to increase without a TDS controller?

Reverse Osmosis ( R.O.)Water Purifiers are being used widely nowadays in India and the rest of the world also for drinking water. The main reason for using Reverse Osmosis (RO) water purifiers is to get most safe drinking water.

As all of us are aware that the water we get for drinking nowadays in towns or cities are coming from either municipal tap water or bore water from an underground source.

And if you are getting water from the tap, the pipes may be very old rusted, dusted & full of corrosion. 

And the Bore well water may also be with all industrial and pesticide pollution material going underground because water with effluent and detergent with other harmful chemicals are being drained in public places or canals or in rivers without any treatment.

Therefore to remove physical, chemical and microbiological impurities from your source water it is necessary to use the most reliable filter to remove these harmful impurities from the water so that it can be drinkable.  

Reverse Osmosis ( R.O.) system works on the principle of  Reversing The Osmotic Pressure with the help of a membrane, so it is very fine purification that even ionic load is also filtered and in the domestic type of RO water purification only 10 % of raw water salts or Total Dissolved Solids (TDS) remain in pure water by default in general and 90% of salt contents flush out.

So this is the reason for being low TDS in RO purified water though it generally happens if you are putting in such raw water in RO which is already low in TDS like River water or tap water 

How to increase TDS without a TDS controller?
 

To increase TDs in RO water nowadays TDS control valve is being fitted and this is the mechanism where some pre-treated water is added to the final treated water and then passed via UV for final disinfection but in this system whole reliability of clean water depends on continuous workability of the UV system 

So another method is called remineralisation means if we fit one mineral cartridge or alkaline filter in post-filtration of any RO system then we can increase the TDS in the final treated water even without fitting the TDS control valve, so this method is preferable and even UV can be fitted here in end-stage for more reliability of water quality.