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Updated: September 20, 2013 15:36 IST

The quality counts

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How do we check whether the water we drink has harmful bacteria in it or not?
The Hindu
How do we check whether the water we drink has harmful bacteria in it or not?

The H2S paper strip test, based on the detection of H2S producing bacteria, is an effective way to test the water that we drink

Water continues to be one of the single largest causes of disease outbreaks especially during the monsoon.

Intermittent supply of water, once in two or three days, can mean that the chlorine used for disinfection by the municipality can disappear by the time it reaches the tap, leading to chances of contamination.

Bore well water is usually not disinfected and in many places, bacterial contamination is reported even if the water comes from great depths.

Private water tankers and bottled water from the local market may also have bacteria in them.

Another major problem identified has been the contamination during storage and handling of water.

How then to check whether the water we drink has harmful bacteria in it or not?

Simple test

The H2S paper strip test, based on the detection of H2S-producing bacteria, is a simple way to find out if e.coli, salmonella, clostridium and other enteric bacteria are present in the water we drink.

A pre-sterilised paper with a culture medium is placed in a 25-ml glass vial with a fill line mark on the bottle.

The water to be tested is carefully added to the vial till the fill line.

The colour of the water in the vial after 48 hours is observed. If the colour stays brown, the water is safe from bacterial contamination and good to drink.

If the water colour goes pitch black, then the water is likely to be bacterially contaminated.

The H2S paper test can also be used to check if a water filter is working well or not by checking the quality after filtration. If water is stored in pots and utensils, this too can be checked.

A test was performed on a famous brand of water filter. While the input water showed bacterial contamination the output water was clean. The filter passed the test.

The students of the government school at Bijuwara village in Bangalore rural district were taught how to use the vial test. They checked the drinking water quality in the school and in their homes.

While many samples were safe, some reported contamination. It was possible to identify the problem and take remedial action and now all the water in the village is safe to drink.


The students also learned about a simple technique called SODIS, or solar disinfection, in which bacteria-contaminated water can be put in clean bottles and left in the sun for six hours. The children found that this was an effective method of disinfecting and purifying water. It should be remembered that the H2S paper strip test tests only for bacterial and not chemical contamination. Similarly SODIS can treat bacteria in water but not chemicals.

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