About field testing kits:
Water is tested in laboratories to find out the minerals present in it along with parameters like pH, conductivity, colour and turbidity. The tests help establish the presence of any parameter and the extent to which it is present in a particular water. Most of the tests are done using the time tested method of titration, using laboratory glassware like burettes, pipettes, conical flasks and beakers. This method still prevails although modern instruments like spectrophotometers, chromatographs, etc have started making their presence felt for testing parameters where the titration method cannot be used.
Since it is not possible to carry delicate glassware out into the field for field tests, several companies/agencies/NGOs/Government laboratories have done a lot of work to bring out kits which use the titration principles but are light, can stand up to rough 'travel' and still give fairly accurate results. These are field test kits which can be used anywhere and by anyone who can read the instructions. Titration involves using a chemical solution of a known strength in a burette to be added to a sample of water to be tested in a beaker/conical flask. A chemical indicator solution is also added to the water before titration. The solution from the burette is added to the sample in carefully controlled drops with the sample being continuously stirred. This addition is stopped when the colour of the sample changes. The burette reading taken after colour change is multiplied by a specific numerical factor. This gives the quantity of the parameter tested for in the water in terms of mg/litre or parts per million (pm). All titration tests are colorimetric tests where a change in colour is an indication that the presence/absence of the parameter being tested had been ascertained.
Most of the field test kits operate on the same principle. The kit consists of a sample bottle with a marking on it to indicate that the sample to be tested must be filled up to that mark. Another bottle contains the required chemical solution (which in a lab would be in the burette). This bottle would have a dropper fitted on it. Depending on the parameter to be tested, there would be a small dropper bottle containing the indicator solution (tests for certain parameters may not need such an indicator).To use this kind of a kit, the sample bottle is first rinsed with the water to be tested and then filled up to the mark. The solution from the dropper bottle is added to this sample after adding the recommended drops of indicator solution, a drop at a time, counting each drop. When the colour of the sample changes, the addition of the solution is stopped, number of drops added is multiplied by a factor given in the instruction manual to arrive at the quantity of the parameter in mg/litre of water or ppm.
Test kits used for testing the bacteriological content in water are slightly different. Some have a bottle in which the sample of water to be tested is put and into which another solution is added. It is then shut and kept for a period of several hours or overnight. If, at the end of this period, the sample has acquired a colour as given in the instructions, it indicates that the sample is bacteriologically contaminated, otherwise not. Another kit used for such tests is called a 'dip slide'. It consists of a slide made of an inert plastic material coated with a nutrient which is kept inside a sealed container. This slide is taken out of the container by breaking the seal of the container, dipped into the sample of water to be tested and then kept aside for several hours or overnight. If, at the end of this period, the slide has acquired or changed colour it is an indication that the sample is contaminated. Tests for bacteriological contamination using such kits only indicate the presence or absence of contamination (also called a GO/NO GO result) and not its extent.
It is important to remember that all such kits have a shelf life. Once this has expired, the kits must not be used as results will be wrong or inconsistent. Given below is a table of the kits available in the market indicating the parameter, name and manufacturer/supplier from whom they can be procured. The accuracy of the results may not be as accurate as those done in a laboratory. It may be in the range of +/- 5. In the table below, where a multiparameter kit is indicated but not the parameters, it is usually for the parameters which determine the potability of water.
About field testing kits: