Top of the range Indian RO purifiers boast of having in addition to RO water purification also UV and UF purifiers in the same water purifier and they proudly call it RO+UV+UF Water Purifier. In the opinion of this author this is a marketing ploy just to get extra money out of the consumers. Let me explain.
We will start with blending UF ultrafiltration water with RO purified water first and then at the end of this page we discuss why a UV after an RO water purifier is total waste of money
From the above flow diagram we have to understand that raw water under pressure is sent to both the RO and UF water purifier and there is a TDS controller to adjust the TDS of the purified water.
Purified water from the UF water purifier will be free of any germs, but all the salts in the raw water remains in the UF purified water. If there is any dangerous salt in the water like Arsenic, then the UF purified water will contain Arsenic. When the TDS controller uses the UF purified water to mix with the low TDS RO water, Arsenic will be introduced into the RO purified water. This defeats the very purpose of having an RO water purifier, which is to get rid of any dangerous dissolved salts in the water. Instead of buying such a water purifier it will be cheaper to buy a UF water purifier which works without electricity and will also be cheaper.
To adjust the TDS of RO water purifier, the better solution will be a remineralizer cartridge to harden water like the 'Taste Enhancer' in the flow diagram below of the Aquaguard Enhance RO+UV. Here purified RO water is passed over remineralising cartridges taste enhancers which usually contains purified Calcium and Magnesium salts, to slightly harden water and also adjust the pH of the RO purified water to make it slightly alkaline. Such alkaline remineralising of water is said to be good for health and also improves the taste of the water.
There is no sense in having an RO water purifier with UV as in the above flow diagrams of both the Kent RO with UV water purifier and the Aquaguard RO wih UV water purifier. RO and UF water purifier filters out all germs and virusus from water and there is no point in having a UV purifier after the RO trying to kill non existant germs, because the water is already very sterile after passing through an RO or UF membrane. In most of these top end water purifiers the purified RO water goes into a holding tank, where the pure RO water will stay for some time.
The RO purifier manufacturer to defend the foolishness of fitting a UV after the RO water purifier might say that the RO purified water, while being stored for a long time in the RO water holding tank may get contaminated with germs on standing for some time. So from where do these germs come to contaminate the water in the RO purifier tank? From the air? If it comes from the air it would have already been breathed in by those living there. There are plenty of bacteria floating around in the air everywhere. But these are harmless germs to which all of us are immune. Nobody needs to be that careful about their drinking water that it has to be 100% sterile.
One more thing to say here. Any infection with germs can be easily cured with antibiotics and the like. So more than germs, what you have to look for in a water purifier is whether it will clean the water of poison chemicals like Arsenic, heavy metals, Nitrates, etc. This is the main job of an RO water purifier, to get rid of any harmful chemicals in the water. While doing the job of removing chemicals from water it also removes all bacteria, viruses, parasites and their eggs.
Just for information, Chemical molecules in water are at least a thousand times smaller than the very smallest bacteria or virus. If an RO water purifier can remove the salt molecules, then removing bacteria and virus will be like childs play for an RO.
So having a UV to purify RO water without germs is, in the opinion of this author, a sales gimmick and simply to take more money from the customers. Do not fall for it.