I’m pretty sure that anyone who has looked at an advertisement of an RO system has seen the words ‘TDS Controller’. I’d like to tell a little more about what this thing is and how it can help you.
A TDS controller, like the name suggests is a device which helps control the TDS level of the water coming out of the RO. The RO process reduces the hardness of the input water by approximately 90%. This means, that for an input of TDS 700, the output will be close to 70.
However, sometimes the source being used for the RO system itself has a low TDS value. Now water having a low TDS value, does not indicate that its pure. Also, the RO system does not just reduce the TDS, it also filters away, microbes and other contaminants from the water. Thus, the water coming from such a setup, with a low input TDS, with have a bitter taste. To prevent this, a TDS controller is installed which allows us to raise the TDS value of the output water.
Now comes the question, how does this work ?
The water going into the RO is split into 2 parts :
Part 1: This part goes into the membrane and undergoes the RO process. This output will be pure water of lower TDS.
Part 2: This water does not go through the RO membrane. It goes through a UF membrane or a UV Chamber, depending on the RO specification of RO+UV+TDS or RO+UV+UF. The output will be water which is pure, but of the same TDS as that of the input water.
The full output of the RO machine is a mixture of Part 1 + Part 2 water. The mixture is controlled through a valve connected to the Part 2 assembly, thus controlling the TDS.
This interestingly, is the main reason, why there is no RO+UV system and that a TDS controller with always be paired with a UV tube or a UF membrane. Attaching a UV tube to water which has already been processed through an RO system, will achieve nothing. But the water being added to control the TDS, needs some purification, because it is essentially raw.
So, in places where the input TDS value is low eg. TDS values of anything below 400, a TDS controller can help give you better tasting water.
Questions Regarding Reverse Osmosis Systems 
How to add tds controller kit to a ro + uv water system?
Please give step by step guide.
nice one..i was not knowing the principle of tds controller..thank you..
Ro paani se jauri minerals bhi nikal deta h like calcium etc…uska kya solution h?
you can add mineral cartridge at the output of processed water.
No it does not.. It keep the balance.
tds controler kitna hona chahiye? maine 8 set krvaya hai its ok or not?
no, its should be at 300 and maximum upto 500
how to know measure tds level
I bought a water purifier having RO+UV system. It does not mention tds controller anywhere. Is it ok? Or tds controller is a necessity? My previous system was RO + UV+ tds controller.
how can be control TDS from waste discharge water !!!!
That means RO’s with TDS controller are not giving 100% pure water because only certain amount is passed through ro membrane and rest is passed through UF membrane which is not as good as RO membrane