On Water Quality Standards and Water Quality Indices

The quality of water is expressed through a number called Water Quality Index. Physico-chemical and Biological parameters available in water under examination are used to arrive at this number. Measured content of the pollutant, ideal content and standard content for safe use determine this number. Whereas the ideal content and measured one are fixed for a sample, the standard content varies from country to country and from agency to agency. Thus, WQI arrived at by using different standards may vary, if the standard values differ. Presently measured results and standard values of different countries / agencies yield drastically varying WQI in some cases in present measurements. The Australian, Canadian, WHO, ICMR and BIS standards give very high values of WQI. The standards of EPA and EU respectively yield WQI, 67 and 64. They are in reasonably good agreement and yield fairly good quality of drinking water.