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Testing Water Purity

Laboratory Testing to Check the Purity of Your Water

To check the purity of water we must carry out a water test in a laboratory.

Here we look at the test results and how to read them. We also look at the maximum permitted levels of chemical, physical and bacterial contamination.

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Is Your Water Contaminated or Impure

Does your water smell when you turn on the tap? Does it look dirty? There may be a lot of contaminants in the water that you are not aware of.

We use water testing as a means of identifying contamination problems which are frequently manifested as smelly or dirty water. We need to be aware that water that appears, smells or (if you are brave enough) tastes innocent enough may well contain hidden nasties.

water testing results

Threats to our water supplies not only come from natural sources or the irresponsible behaviour by industrialists but also from a basic lack of understanding among the general population and the lack of the imposition of hygiene standards. Unbeknown to many people, most countries of the world have very comprehensive ranges of standards that cover everything from reinforced concrete to food standards. For our own safety it is advisable to take our own measures to look after ourselves.

Water laboratory test results and how to read them

So let's look at water tests and what they can tell us. You can see a typical Laboratory report here. We'll keep it simple and start with a sample of a water test result.

Item Measure Recommended Test Result
Physical Characteristics
Smell Nasal No smell No smell
Taste Oral No taste No taste
Colour TCU 50 14
Temperature Degrees C Ambient + or - 3c 27 C
Turbidity (cloudiness) NTU 25 6
Total Disolved solids TDS in mg/L (miligrams per litre) 50 14
Chemical Characteristics
pH (acidity) mg/L 6.5 to 9.0 6.96
Potassium permanganate (KMnO4) mg/L 10 5.06
Calcium Carbonate (CaCO3) mg/L 500 5.08
Chloride (Cl) mg/L 600 9
Flouride (F) mg/L 1.5 0.84
Sulphate (SO4) mg/L 400 59
Sulphide (as H2S) mg/L 0.05 0.002
Cianide (CN mg/L 0.1 0.002
Nitrate (NO3N) mg/L 10 15.5
Nitride (ion NO2) mg/L 1.0 0.08
Iron (FE) mg/L 1.0 0.15
Aluminium (Al) mg/L 0.2 0.11
Manganese (Mn) mg/L 0.5 0.01
Chromium (Cr) mg/L 0.05 0.03
Zinc (Zn) mg/L 15 16.9
Copper (Cu) mg/L 1.0 0.03
Lead (Pb) mg/L 0.05 1.00
Residual Chlorine mg/L 5 0.01
Silver (Ag) mg/L 0.05 -
Detergent mg/L 0.5 -
Arsenic (As) mg/L 0.05 -
Organochlorine mg/L - -
Organophosphate mg/L - -
Carbamate mg/L - -
Coliform MPN per 100ml 0 2400
Fecal Coli MPN per 100ml 0 21

The first column indicates the test carried out. The second column is the units of measurement. The third column is the recommended maximum level or the acceptable range. The final column is the actual test result and the reading should fall within the parameters of the third column.

Physical condition of the water

The first section of the test report tells us about the physical condition of the water. Does it smell? Does it taste? Is it coloured (TCU or True Colour Units) or cloudy (NTU or Nephelometric Turbidity Units) and finally a general measure of the volume of contaminants that are floating around in it (TDS or Total Dissolved Solids).

Please note that tasting water from a well in Bali is not a good idea and is rather like playing Russian roulette with a machine gun. It is also fairly common that water in paradise looks cloudy or smells like a Gorilla's armpit on a bad day, a hint that perhaps the water is not quite as pure as it could be. Water colour is measured by comparing with test samples and the darker the water the higher the figure. For those of you who like filling your head with useless information on the chance that a quizz question will come up you will be really excited to learn that the turpidity (cloudiness) of water is measured with a nephelometer.

The next section starts with a measure of the ph or acidity of the water, a factor well understood by pool owners and those people who find that metal pipes, particularly metal u bends under washbasins, don't last very long.

Chemical analysis of the water

The section then provides a chemical analysis of the many contaminants in the water. Now before you start panicking I should point out that all water contains contaminants, in fact it would be pretty boring stuff if they weren't there. The key factor is the level of contamination, too much of anything is not good for you.

High TDS and high levels of calcium or manganese are consistent with hard water which can choke up your kettle, toilets and those little holes in the showerhead that become clogged and drive you insane first thing in the morning as you run around trying to find a jet that works.

Most contaminants are harmless and some, such as iron, zinc, copper and manganese, our hard working bodies need. Iron keeps the anaemia away and fluoride is added to our toothpaste to put dentists out of work. A glass of dirty water is far cheaper than those expensive mineral supplements you by at the chemists these days.

Other contaminants we are probably better off without, arsenic might add flavour but does have a tendency to hasten the most inevitable. Heavy metals, particularly lead, plutonium and mercury are, of course, very toxic with the serious problem that they can build up in your body over many years.

The next section covers toxins from pesticides and insecticides which may come from agricultural sprays.

Bacterial analysis to find organic contamination

The final section is the bacteriology analysis which checks for Coliform and Ecoli contamination. These are "indicator" tests to show if the water has sewage contamination. They should come out as zero, if a positive reading is found this may mean contamination by any number of nasty bugs, individual tests for each of the many types of pathogen would be extensive and costly hence the use of these "indicator" tests.

If we look at the above sample several things are indicated. The first is that the water has bacterial contamination and both Coliform and Ecoli have been found. The Coliform reading of greater than or equal to 2,400 MPN per 100m/l is the top of the scale. The chemical analysis indicates nitrate levels being high which is also consistent with bacterial contamination. We can assume that the contamination is probably due to septic discharge getting into the water table. See the recent article "Septic Understandings". This is a common problem with poorly installed and badly maintained septic tanks, wells and bores (and remember not necessarily your own but those of other people in the surrounding area).

Of more concern in the above results is a high zinc content and far worse a high lead content. The reading is 20 times the maximum "safe" level.

This water is contaminated both bacterially and chemically and arrangements should be made to find a "clean" water source. It is probably also a good idea if authorities and neighbours are alerted as anyone on the same underground watercourse (if that is what it is) can be exposed to the same danger.

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Copyright © Phil Wilson January 2009
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