How to make Drinking Water Microbiologically Safe?

We all know that water-borne diseases are mostly caused by the contamination of drinking water by faecal matter. Human excreta contains disease causing bacteria along with harmful coliforms and E. coli. It is easy to detect coliforms in water than the actual disease causing bacteria but this method needs an expert and laboratory facilities. Since H2S producing organisms are also associated with coliforms, it is much easier to detect the same that gives off the typical rotten egg smell. This procedure does not need high expertise.

To detect the indication of disease-causing organism in drinking water.

Materials / Equipment Required

 Sl #
 1  Peptone  40gm
 2  Dipotassium hydrogen phosphate  3gm
 3  Ferric Ammonium Citrate  1.5gm
 4  Sodium Thiosulphate  2gm
 5  Teepol  2ml
 6  Water  100ml
 7  Plastic Bottle  30ml Capacity
 8  Tissue Paper  80cm2
 9  Marker Pen  1


  1. First dissolve serial no. 2, 3 and 4 in 100 ml water by mild heating, then add Peptone.
  2. Observe the solution till it develops a uniform suspension and then add Teepol. If this sequence is not followed, it infers that the ingredients did not dissolved properly.
  3. Dispense 1 ml of this solution into 30 ml capacity bottle. You can also use 80 cm2 tissue paper, fold it and dip it into the concentrated medium (it will absorb 1 ml) and then place it in the 30 ml bottle.
  4. Loosely cap it and autoclave (121’C for 15 minutes) or use pressure cooker with full pressure on for 15 minutes, to sterilize.
  5. After cooling, tighten the cap of the bottle and now it is ready for use. Remember, the cap should not be opened till you use it, since it may contaminate the bottle if opened. Mark 20 ml level on the outside of the bottle with a marker pen.

Experiment and Data Analysis

  1. Fill the test water up to 20 ml mark in the bottle and leave it at room temperature (25-44’C). If the room temperature is too low, keep it in your pocket while sleeping, or keep under a light bulb.
  2. Observe the change in colour of the bottle after 24 hours and 48 hours. If it turns black then the water is contaminated and not fit for drinking.


All the bottles turning black may have disease carrying germs, hence they have to be boiled before disposing or kept in 5% phenyl overnight or the liquid portion is disposed off in the toilet.
Experiments and Follow-up Action

You can also test chlorinated water. Bleaching powder has 25-33% free chlorine. Chlorine at 2-4 parts per million can kill most germs in 30 minutes.

Chlorine can generate minute quantities of carcinogens (substances that cause cancer). So do not expose yourself to the chemical for a long time.

You should use your own skills and innovation to test and experiment with newer methods of disinfecting water. Ask for your teacher’s help and advice to carry out experiments in your school.

Manja et al. (1982) ‘Simple field test for the detection of faecal pollution of drinking water’, Bulletin WHO 60:797-801.


Source: Harness water resources for a better future - Activity Guide for the 13th National Children's Science Congress