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| Sep 03, 2006 10:21 am |
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[Fufaji se poochcho] - All about water purifiers. |
Basab Ghosh
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As we are still beating around the bush, let me say what I understand with my limited knowledge of water and it's purification systems......
1. Most domestic purification systems these days come with a sediment filter and an activated carbon filter. The first one filters out particles over 5 micron (0.005 mm) in size (which eliminates most undissolved particles) and the second one removes chlorine and other halogens along with related odours. Some companies provide a pre-sediment filter of 20 micron size.
3. In conventional systems (e.g. aquaguard), this is followed by an UV filter, in which the UV light deactivates bacterias & viruses (about 99%), but they remain in the water. The downside in these systems is that they do not lower the TDS (Total dissolved solids) of water or any other dissolved contaminants. So brackish water remains brackish. One can use these systems only if the tap water has a TDS less than 500 ppm (parts per million). What the selling companies do not mention is that even then, the water is not safe for drinking if heavy metals or arsenic are dissolved in the water.
4. The RO (reverse osmosis) systems remove all (99.9%) particulates above 0.0001 micron, including dissolved solids, bacteria & viruses, which makes the water almost distilled water quality and consequently also tasteless.
5. Some companies provide post RO treatment to put back some minerals and taste into the water, some do a post RO UV filter to guard against possible failure of the RO membrane. Some don't provide any post RO treatment. Point to remember, the RO process rejects about 75% of the input water and lets in only about 25% water. For some taste in water, one needs a minimum TDS of 50 ppm.
6. Higher the TDS, lower the life of the membrane, even with membrane flushing system, which most lower end seller do not have. Many do not have the automatic flushing system. I am not sure back flushing is employed in RO systems or whether that is possible.
7. Domestic RO systems can generally handle upto 1500 ppm TDS, beyond which most won't guarantee their system. One or two handle up to 4000 ppm, but that is about the limit. Industrial RO systems can be designed to handle even higher TDS levels (and Soeb, RO based desalination plants are now being installed), but at a very high cost.
8. The so called mineral RO systems probably bypasses a small part of the input water directly into post RO filters. In these cases, a post RO UV treatment becomes imperative to kill the germs carried by this untreated water.
Well, with this as input, Lalit can advise us what would be an ideal domestic RO system and compare between brands and their products.Private Reply to Basab Ghosh (new win) |
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