What is the best way to test water quality for your purpose? This article discusses and compares commonly used scientific water quality testing kits that can be used to quantify the quality of various water parameters.
1. Biological Indicators
Biological monitoring metrics is the simplest and least expensive method. It involves monitoring the presence and abundance of members of bio-indicators common to the area, eg:
- Insects such as the mayfly, stone-fly and caddisfly. Generally, the greater the number found, the better the water quality. Organisations in the United States, such as EPA offer guidance on developing a monitoring program and identifying members of these and other aquatic insect orders.
- Bivalve molluscs are largely used as bio-indicators to monitor the health of aquatic environments in both fresh water and the marine environments. A typical project is the Mussel Watch Programme, but today they are used worldwide.
- Benthic macro-invertebrates (such as the aquatic earthworm) is a bio-monitoring tool that is used by the Southern African Scoring System (SASS) system to measure river health. miniSASS is a simpler scoring system that can be used by anyone, even school children.
2. Test Strips
Test strips for various water quality parameters are available, such as pH, chlorine, etc. Here you dip a little paper strip with graduated colours into your water sample and match it with a colour on a printed list, to determine the level of the parameter.
Test strips are inexpensive, quick and easy to use, but offer the least accuracy and precision, due to printing variations, poor resolution and the variability of the human eye.
3. Titration / Drop Test Kits
This simple method uses visual titration. A chemical (reagent) is added to a water sample and the concentration is then determined by counting the number of reagent drops or tablets required to induce a colour change.
It offers higher accuracy than test strips, but involves some technical ability, because careful counting, basic calculations and and the ability of the human eye will be required. It is a rapid, economical test for all chemical parameters, such as pH.
The exception to the rapidity of the testing are microbiological tests, such as those for coliform / e.coli. These require incubation for 12 – 48 hours.
4. ATP / Luminescence Tests
A luminometer and a consumable testing device can be used to instantly measure the presence or absence of bacterial contamination in water. It is ideal for quick screening, but more in-depth and time consuming testing will need to be undertaken if more detail is required.
Here the initial cost of the luminometer instrument is costly, but replacement consumables less expensive.
5. Electro-Chemical Testers
These testers comprise of a pen-type, hand-held or bench-top meter and an electrode. They are very useful for in-the-field / in-situ testing and are usually rugged and waterproof. However, the electrode needs to be carefully maintained and will need to be replaced every few months to few years, depending on circumstances.
Only a few key parameters can be measured in this way, such as pH, electrical conductivity, dissolved oxygen, total dissolved solids and salt. The many other water quality parameters will need to be measured using another method.
6. Colorimetric / Comparator Test Kits
Colorimeters or comparators have been widely used by companies for well over 100 years, to measure the quality of water. A reagent is added to a known sample of water. The intensity of colour is then compared with coloured plastic or glass filters, in order to see the concentration of chemical present in the water (eg. Chlorine).
These require some skill to use and are dependent on the variability of the human eye, which means that it is less accurate than a digital photometer.
Comparator discs are available in plastic and glass. There are hundreds of different discs available, to measure different parameters and different ranges. Plastic discs are less expensive than glass discs, but do not last as long. The glass discs are very stable, Selectech has customers who have used them for decades.
7. Photometric Test Kits
The most popular option today is the modern electronic photometer. This is the easiest and most accurate way to test water, if you are performing frequent water testing, or require precise results.
The micro-processor controlled digital systems have highly reproducible results as they are not dependent on the human eye. No special training is required to use a photometer that comes with step-by-step instructions.
After the initial outlay for the instrument, the cost per test for both the comparators and photometers is lower than many other products.
The cost per test for a glass comparator test kit vs a digital photometer is very similar.
For specialised water testing that requires many parameters to be tested with the highest precision levels, a spectrophotometer is the ultimate instrument.
This instrument features a dual beam optical system, one of which is reference beam, for above average accuracy. UV light and / or visible light can be used. Further functions can include measurement of transmission and absorbance, scanning of spectra and kinetics analysis.
Newer photometers and spectrophotometers are equipped with the latest pre-programmed methods that can be updated via an internet connection.
Further technological features include interfaces to a PC, blue-tooth, USB and Ethernet.
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