Home water purifiers; Know the filters inside

Home water purifiers, which one to choose? Know the filters inside

Water purification could take place at three places, the place of production, the point of entry to house and the point of use. Municipality takes care of purification at the point of production. If you are using water from well or river directly, a point of entry whole house filter would be ideal. When you are using water supplied by government you need not worry about chemical or biological contamination. The only area you need to consider is the point of use.

This section mainly discusses the point of use (POU) purifiers. But before we discuss water filters, let us consider one basic question.

Why you should buy a home water purifier?

1.     Cheaper

·          A small family in UAE spends AED 2500 for buying large bottles; cost is more when we buy smaller bottles

·         Empty bottles occupy three to five square meters of office / house space costing a minimum of AED 5000 in annual rent.

2.     Convenient

·         No need to wait for the sales men

·         No need to lift heavy water bottle

·         A purifier gives non-stop water supply

·         The machine in your kitchen is more reliable than one sits several miles away

3.     Earth friendly

·         No wastage of empty bottles

·         No transportation cost

Now, let’s come back to the main issue. One purifying machine could contain different filters inside. People mainly go for bottled water because they do not know that the home filters can do the job better. If you go to buy a water purifier without gathering enough information, you could either waste a lot of money for features which you do not require or buy something that does not solve your problem. The worst part is that you could continue to use bottled water.

Filter size: If you read the sticker on a filter, you would notice the pre size of filter. Smaller size is better. A filter pore size is often mentioned in terms of micron. One micron is 1/1000,000^th of a metre. In other words 1000 micron is one millimeter. A diameter of a human hair is approximately 100 micron. Any filter with pore size around 5 microns or below can give you clean looking water, but most of the microorganisms pass through the filter.

Following are the common filter types:

1.     Sediment filters: Sediment filters, as mentioned above, are only meant for removing larger suspended particles from water. These filters are pre-treatment filters. Sediment filters are usually made of polymer, cloth like material. PP filter means Poly Poplin (textile) filter. They have pore size around 5 microns. Remember, 5 micron filters are only pre treatment filters. They are useful inside a purifier. Never use a sediment filter as a stand-alone unit.

2.     Activated Carbon Filters: Carbon is very effective in removing most impurities from water including chlorine. Carbon is activated by passing oxidizing gases at very high temperature to create pores in the carbon which substantially increases the surface area to trap impurities. Surface area of one pound of activated carbon is said to range from 50 to 150 acres which makes it very powerful in capturing the impurities. Activated carbon stops impurities in two ways. First it does not allow particles above the pore size to pass through. Secondly, it traps chlorine and other contaminants inside the pores. There are two types of activated carbon:

·         Granular Activated Carbon (GAC) Filters: GAC Filters made by packing lose carbon granules to allow the water to pass through it. GAC filters allow faster water flow. But they are less effective compared to Solid Block Filters.

·         Solid Block Activated (SBAC) Carbon: As the name indicates carbon is bonded together to form a single solid block. Solid block filters provide larger surface area compared to GAC filters. Smaller pore size of SBAC filters allow better filtering.

Carbon filters do not remove fluoride and arsenic. Only reverse osmosis is effective where these contaminants are present.

3.     Reverse Osmosis (RO) Filters: Osmosis is the process by which plants roots absorb water from surrounding soil. When liquids of two densities are separated by a semi permeable membrane the high density liquid will absorb a low density liquid. In reverse osmosis filters, this process is altered by applying pressure on the high density side. To put it simply, contaminated water is fed in using a pressure pump in to one chamber. RO membrane does not allow impurities to pass through. About one fourth of the water comes out clean through the RO filter. The remaining rejected water goes out though the outlet valve.

See the diagram below:

Reverse Osmosis the possibly the most effective way of water purification. It can remove bacteria, virus and dissolved salts. RO is the only filter which can produce fresh water from sea water.

The main disadvantage of RO filter is the water rejection. The maximum output of clean water is only twenty five percent of the input water. It is does not matter when you are filtering sea water. But when water availability is scarce, you cannot afford to waste that much water. Another issue is the need of electricity. There is a small electric pump to apply pressure on the input water. The filter cannot be used where electricity is not available. RO filter require regular maintenance. Excessive chemicals damage the filter. Good pre-filtering is essential to minimize chemical concentration of input water.

4.     UV Filters

Ultra Violet (UV) light stops the reproduction of bacteria and viruses. These filters are effective only against microorganisms. They do not remove other impurities. We cannot use it as stand-alone unit. However it is very useful in combination with other filters such as carbon or polymer filters.

Apart from the above basic purification methods there are several other technologies used independently or in combination with the above.

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