Saturday, February 12, 2011

Evaluating the necessity and usefulness of water filters for domestic tap water

My above project has finally concluded after months of experimental work by my project team.

Due to the popularity of water filters in the market these past years, I thought it will be interesting to find out more about them, especially if they are necessary and useful.

Filter 1

Figure: Home-made gravity filter using Doulton Supersterasyl filter candle (the white thingy in the middle) - ceramic (diatomaceous earth) filter impregnated with silver and incorporating a granular carbon core

Filter 2

Figure: Pressure filter train utilising standard 10-in filter housing. Order of filtration from input to output: pleated 5-um, twisted yarn 1-um, granular activated carbon (GAC), ion-exchange, fluoride reduction, pleated 0.5-um, pleated 0.35-um

Tap water was sampled from 4 different tertiary institutions well distributed spatially in Singapore. It was then allowed to run through the 2 types of filters. The raw tap water, filtered water from filter 1 and filtered water from filter 2 were tested for the following parameters - turbidity, pH, conductivity, nitrate, fluoride, total hardness, chloride, sulphate, phosphate, iron, manganese, copper, aluminium, total chlorine, aerobic bacteria count, lead. Most of the above parameters are similar to the routine testing done by PUB.

Figure: Portable water quality with typical PUB values and WHO guidelines

Tap Water Results
From the above table, you may have noticed that most of the PUB's values are well below the limits under WHO guidelines. Well folks, good news! Most of our results lie within PUB's values so PUB is not kidding in providing quality tap water. (However, WHO guidelines are not omnipotent as you may have read in my previous post - water filters in Singapore.)

For the astute reader, you may have noticed the word "most". For 2 institutions, copper content in tap water is at 0.21mg/L and 0.15mg/L, respectively - much higher than the PUB value of 0.05mg/L. In case you start jumping to the wrong conclusion, don't forget that the values above only apply to water coming of PUB's waterworks. The water still has to travel through miles of piping through the distribution network and store at various locations along the way before ending up at your tap. Lots of things can go wrong - leaking lines, corroded piping, poorly maintained tanks etc. Older buildings probably have corroding copper pipes which jack up the copper content in tap water.

The other parameter of interest is fluoride. Surprisingly, 2 of the institutions have tap water containing only 0.1mg/L fluoride while the other 2 just meet the minimum of 0.4mg/L as given by PUB. Officially, fluoride is added (yes, it is not a contaminant but is intentionally added) into water to fight tooth decay. Are we getting enough fluoride in our water for it to do its job? On the other side of the story, critics have fought against fluoridation at any level as we are already getting enough fluoride in our diet and taking in more can compromise our health - see fluorosis.

The next big thing in water is chlorine. Relax... our water is not overchlorinated. Instead, the tap water results are in the range of 0.05 - 0.15mg/L. Different sources cite different values for adequate chlorination at the end user, ranging from 0.2 - 0.5mg/L or even more. Our results are rather low so the question is whether our tap water is adequately disinfected. As you would have guessed, there is another side of the story - consuming chlorinated water has been linked to several cancers and heart disease. It is also inked to the production of trihalomethanes (THM) and haloacetic acids (HAA) in water, both of which are likely carcinogens. Hence, a low level of chlorine in tap water may actually be good news.

2 institutions have very high levels of bacteria but don't be alarmed. We are measuring aerobic bacteria and not an indicator bacteria like faecal coliform or Enterococcus. Of course, the older the distribution network and the poorer maintained it is, you are likely to see more bugs in your tap water. Actually, the purpose of measuring aerobic bacteria is to gauge the effectiveness of filtration by comparing the values before and after filtration.

Filtration Results
Frankly, because our tap water is so clean, the filters we tested could not perform as well as they could have or were certified for. Certification e.g. NSF/ANSI standard 42 or 53 requires a certain challenge inflow concentration. If the outflow concentration falls by a certain percentage, say 90%, the device has passed the test. But if the inflow concentration is already very low, a 90% reduction is not likely to be achieved.

The gravity filter appears significantly more capable at removing chlorine (25%), iron (92%), manganese (34%) and aluminium (55%) while the pressure filter seems better at reducing nitrate (42%), fluoride (58%), hardness (35%), chloride (40%), copper (75%) and bacteria (> 94%).

However, sulphate does not appear to be significantly reduced by either filter (< 7%).

Final thoughts
Are water filters necessary?

If you trust WHO guidelines and PUB seems to be doing a good job at providing quality water consistently, then no, you probably don't need them.

But if you feel that for whatever reason, WHO guidelines (or PUB typical values) are not adequate at safeguarding your health, by all means get a filter but know that to reduce the contaminant level even further, a filter probably won't cut it. You probably will need reverse osmosis, distillation or air-to-water units to give you the next level of water purity. In any case, it is good to be sure of exactly what you are concerned about e.g. chlorine, fluoride. Better still, send samples of your tap water to a commercial lab for analysis of that particular concern. AND submit for analysis another sample after going through your preferred treatment. You should then be able to have a good idea if your treatment unit is working up to your expectations.

Of course, you may suspect that there is something wrong with the distribution network. My advice is the same - be clear of your concern, analyse your water and get a treatment unit only if necessary, preferrably with a follow-up analysis of your treated water.


Nalgene Navel said...

Hi! Great article!

I came across your site when i was searching on water quality in singapore. I had found gooey residue trapped in my shower head filter two days ago and now concerned about the water that I'm receiving from the HDB water tanks. I've taken pictures of it.

Could you tell me where can i get water in my apartment analysed? Thanks in advance!

CK said...

Hi, you can try searching through the yellow pages for commercial testing labs in Singapore. The better known ones are PSB, Setsco, SGS Testing. Please note that I am in no way endorsing them by their mention here.