The Bureau of Indian Standards has prescribed the specifications for potable/drinking water.
The mineral water is supposed to contain naturally occurring minerals within the permissible limits of potable water. Even though there are about 30 parameters which have to be checked, the most critical is the biological contamination of E. Coli bacteria. There are various methods for the identification of E. Coli, but it will take a minimum of 18 to 30 hours to know the result.
Two ready kits are available wherein you have to just add 50 ml of water sample to a culture media (premixed chemicals). One such kit is developed by the Defence Food Research Laboratory (DFRL), Mysore, and the other by E. Merck, Germany. With these kits the results can be known in 18 hours.
It is suggested that the Government should check all the parameters of mineral water available in the market on a random basis, as in the case of liquor, as testing at the consumer end is time consuming and costly.
Dissolved salts in water affect its electrical conductivity and so a quick test to find the purity of mineral water would be to measure the conductivity.
A number of conductivity meters are available in the market and the best one would be that with a conductivity range of 0-300 micro mhos per cm.
The test can give quick results: if the water’s conductivity is around 200 micro mhos/cm, then the total dissolved solids (TDS) is about 100 ppm, if it is 250 micro mhos/cm then the TDS level is 125 ppm.
These figures may be compared with the TDS values printed on the bottle’s label by the manufacturers.
This will test for the amount of dissolved salts only and not for other contaminations such as by bacteria.
When a drop of water (at room temperature, 30 degrees centigrade) falls on a hot plate (at a temperature of say 150-200 degrees centigrade), the water begins to ‘dance’ around on the plate because of the formation of a layer of steam, at the interface of the drop and the late, which acts as a cushion. When the drop touches the plate, the bottom layer of water in the drop is suddenly heated to more than 100 degrees centigrade leading to the formation of steam at the interface.
Steam not being a good conductor of heat, does not allow the plate’s heat to flow easily into the drop. So, as we move up from that interface, into the drop, the temperature falls down.
The layer immediately above the steam will be of boiling water. In the outer top layer, called the free convection zone, water is heated slightly. At any point of time, the water tries to rest on the plate but the steam holds it up by acting like a cushion.
As a part f the steam leaks out sideways, certain amount of water flows in to fill gap and gets vaporized. This process continues till the water drop is completely vaporized or the hot plate is cooled to below 100 degrees centigrade.
All the natural water contains dissolved ions (positive valency anions and negative valency captions) within them.
