Which type of water purifier I should go for

Water Purifiers reviewed

Know about technology:

In general, domestic water purifiers can be divided in following categories.

Ultra Violate (UV)
Ultra Filtration (UF)
Reverse Osmosis (RO)
Chemical Dosing based (CD)

UV works on the principle of bombarding the water with UV rays. Initially it was thought that UV kills the micro organisms. But the current thinking is that it only deactivates them, or at least some of them, who can get activated again after a few hours. (it is also possible that this is a sales gimmick by the competitor systems). In any case, UV is OK if you are going to use the purified water immediately, without storing it for long.

UF filters the water through a very fine membrane which removes all bacteria and viruses. Of course it removes all suspended impurities and even some colloidal impurities. (what is a Colloid ? Look up in google). But UF will NOT remove dissolved impurities.

RO is the only system that removes even the dissolved impurities. RO is required if the Total Dissolved Solids (TDS) exceeds a certain value. (what is the upper limit ? Look for discussion on that elsewhere in IWP). RO is also suggested if you have reasons to believe that your water may be contaminated with pesticides/ heavy metals/ industrial effluents.

A problem with RO is, it needs a lot of water. It divides the input water in two parts, and forces the dissolved solids out from one part in to other. Thus, the output comprises two streams of water – a “clean” stream with low TDS and cleaned of other impurities too. And a “reject” stream that is even more dirty than the input water. Typically, an input of 3 liters will give 1 liter of clean water and 2 liters of “reject”. Theoretically, the “reject” water can be used for mopping the floor etc. but few have the discipline to do that.

Reduction of TDS changes the taste and pH of water, and it is not good to reduce the TDS too low. Some manufacturers make a hybrid machine that combines RO with either UV or UF. Bulk of the water is processed by RO, to remove dissolved solids; and some is processed by either UF or UV, to kill micro-organisms, but retaining the dissolved solids. The two are combined to restore the dissolved solids to some lower limit. The ratio of mixing the two can be controlled by user.

The simplest and cheapest purifiers are the ones that dose the water with a chemical to kill micro organisms. Most common chemicals used are iodine based or chlorine based. Using an iodine based doser could have some implications for persons suffering from thyroid related problems. Consult your doctor before using such a purifier.

The descending order of cost is RO, UV, UF, Chemicals. RO is typically 10,000 or more, while Chemical based are less than 2000. UV and RO require electricity to operate. UF and chemical based (usually) do not require electricity.

All purifiers in addition to the main processor which is UF/UV or RO, invariably have a coarse pre-filter to remove larger suspended impurities; an activated charcoal processor that removes bad odour and colour – particularly the type caused by decaying vegetable matter in source water; and a post filtering “taste conditioner”. This is what is meant by “4-stage” water purifiers.

For selection, it is not really necessary to get the water tested in a lab. Start with RO. Call the dealer of any RO system for a demo. He will come with a simple portable TDS meter and will measure the TDS at your house. If it is more than about 500 (the limit is debatable), then you need RO. Else, RO is ruled out. That leaves only the micro biological impurities. Go for a UV or UF if your budget is at least 5000/- and a chemical based if the budget is less than 2000/-. As aforesaid, consult a doctor regarding any specific health problems and contra-indications of ALL your family members, before using a chemical based purifier.

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