Q: Which is cheaper in the long run, installing a home water purification system or buying drinking water from water stations and the supermarkets? Also, what’s the difference between distilled and mineral water?

Ina R., Angeles City

A: In the long run, installing a household water purification device brought from an appliance store and purifying water at home will probably be cheaper than buying bottled or purified water from supermarkets and commercial water stations on a regular basis. However, most household purification devices do not purify water as effectively as those systems used by commercial water stations.

The idea behind water purification is to make water safe for human consumption by removing contaminants that are dangerous to health, which means pathogens or disease-causing microorganisms, and chemical and physical impurities. To do this, most of the currently available household water purification devices make water pass through one or more of the following: a mechanical filter element, some absorbent material (usually activated charcoal) and ultraviolet (UV) light.

The mechanical filter element is supposed to filter-out microorganisms. Unfortunately, the pores of the filter element in most of these purifiers are not small enough to do the job. Water-borne pathogens are mostly bacteria or viruses. Bacteria are minute organisms; most are in the boundary of one micro (one-millionth of a meter) in size. Viruses, like those causing viral hepatitis, are even much smaller. Thus, to effectively filter out pathogens, the pores of the filter element should be less than one micron in diameter. Although there are such filters, they are very expensive. Besides, they are impractical because they easily get clogged, which means they need to be cleaned or replaced often.

As regards ultraviolet light, it is true that exposure to ultraviolet (UV) light kills most bacteria, but it takes many minutes to hours to do so. Most household water purifiers expose water to UV light very briefly (few seconds at the most), which is simply not enough to eliminate germs.

The only thing that the average household water purifier does is to make water smell and taste better. The mechanical filter element and the absorbent in these purifiers are able to remove big particles, sediments, and dissolved obnoxious gases, and perhaps even chlorine (in areas where the water is chlorinated), making the water more palatable.

The real effective household water purifiers are very expensive and difficult to maintain, that is why it is probably more practical to simply buy drinking water from supermarkets and duly certified water stations.

Now, let me answer your second question. Mineral water is water taken from natural sources. It contains some ions and minerals. Distilled water, on the other hand, is a form of de-mineralized water. It is water that has been purified by distillation, which involves vaporizing water by heating, followed by condensation. Incidentally, another popular way of de-mineralizing water is by reverse osmosis, which uses filters.

De-mineralized water is free of harmful contaminants. Unfortunately, it is also free of dissolved minerals that natural water contains. Which means, if you drink de-mineralized water regularly, then, you deprive your body of a good source of micronutrients (minerals, in particular).

Many experts say that the best water to drink is mineral water that has been collected, bottled, handled and transported properly to ensure against contamination.

(E-mail inquiries on health matters to: medical_notes@yahoo.com or wellbeing@mb.com.ph))