There are many varieties of water filters available in Indian market. But here I will be talking about the most widely used aquaguard type water purifier ? having 3 stage filtration system. There are at least 10 different brands of these selling ? aquaguard, kenstar, phillips etc.
All these use following 3 stages of filtration :
1) Dust filter (mud and small particles) ? A fine mesh cloth / cotton cartridge
2) Carbon / Charcoal filter ? to stop insipid tastes, absorb chemicals etc.
3) Ultraviolet radiation to kill germs
First we will talk about no. 1 and 2 as its very simple and no technology involved.
There will be a dust filter with fine mesh of cotton weaved cartridge, which you can clean from time to time and replace when needed. It ensures that large suspended particles do not enter.
2nd stage is a carbon filter. This is mainly to absorb some insipid taste in drinking water, basically chemicals. If you use ground (tube well / hand pump) water from different places, it will all taste different due to soil nature ( minerals in soil ). The carbon filter absorbs a large part of it, so water tastes better.
There are also 2 filter discs before and after carbon ? made of finely weaved synthetic fiber . This is to hold loose carbon pieces in place and also ensures that carbon particles are not carried to 3rd stage.
Up to 2nd stage of filtration, all brands in the market have same results and they are no better than Mahatma Gandhi?s filter which he designed for poor villagers of India. Believe me I have used Gandhi Ji?s Charkha and water filter.
Now lets talk about 3rd stage, the UV radiation. There is a wide misconception of its effectiveness. No company will publish its test results and will talk big about their brands and effectiveness of giving you Amrit instead of drinking water.
Now I will not go into details of UV radiation with technical terms as it will be boring for you to read, but some insight into what we are looking at. UV radiation is of 3 types depending on wavelength and all 3 radiation has its different usage. For our use to kill bacteria, the wavelength of UV light must be 253.7 nano meters or less. At this wavelength UV light does not kill bacteria but cause photochemical damage to DNA and RNA within micro organism and render them ineffective for multiplying and cause any damage. In vague terms we call it killing bacteria.
The energy required to kill micro organisms is a product of the UV light's intensity and exposure time. This energy is measured in micro-watt seconds per square centimeter.
Intensity X Exposure Time = microWatt Seconds/cm2
The chart below illustrates the typical energy necessary to kill some common bacteria & viruses,
UV Energy Required for 99% Kill Rate
BACTERIA mW S/cm2
Bacillus anthracis 8700
Corynebacterium diptheriae 6500
Escherichia coli 7000
Legionella pneumophila (Legionnaires Disease) 3800
Leptospira interrogans (Infectious Jaundice) 6000
Salmonella enteritidis 7600
Salmonella typhosa (Thyphoid Fever) 6000
Shigella dysenteriae (Dysentery) 4200
Vibrio cholerae (Cholera) 6500
VIRUS
Bacteriophage (E. Coli) 6600
Hepatitis virus 8000
Influenza virus 6600
From the above you can see that killing bacteria depends on UV exposure time and intensity. The UV cylindrical tube chamber has about 250 ml of water capacity ( 1 glass of water), because half of it is occupied by UV tube and glass casing around it. Roughly one glass fills in about a minute, ie 60 secs.
On an estimate the water that is coming out has an exposure of 60 secs of UV light. I do not have a photometer to measure the intensity of UV light, as at the moment I am sailing on ship. And also I can not measure the wavelength of UV light.
Probably some one having access to good physics laboratory can help me out. I remember an NGO laboratory in Delhi which talked much about pesticides in coke and pepsi.
The above was just to educate you about some facts. In 1993 I checked aquaguard?s test result by some institute in Pune, which the aquaguard vendor hesitatingly showed to me after pulling him about purity of water. The test result clearly mentioned ? It does not eliminate E. Histolytica and B. Coli, the 2 widely spread germs responsible for your stomach upset.
Now we have to live with what is available in the market. They talk about electronic eye monitoring for purity, e boiling and there are models available which will notify the service centre about any problem in water filter by internet etc. Its all gimmicks and drinking water does not become better by all these. The electronic eye is nothing but simple LDR (light dependent resistance - photocell). It can be set for any value by preset potentiometer.
What they have done is that if due to suspended particles, the water becomes less transparent and intensity of UV light falling on LDR reduces by 5 %, it will switch off the flow of water. In other words, if UV light is fused, it will also stop the flow. So they call it 95% purity. Now a situation like that will never arise. For the water to be dirty enough to stop 5 % of light, your 2 earlier filters would have clogged much earlier and there will be no flow of water at all.
In new models of water filter, they have tried to make it sleek and good looking but compromising on quality. They have combined dust filter and carbon filter in one chamber, so cleaning is by their technician only and has to be done more often as filtration chambers are half the size now. For a technology so simple, market price of Rs 5,000 plus is too high. So remember, all brands give you same quality, you can choose by look and price tag.
