A general classification of water quality in Indian context

Water quality criteria are developed on the basis of scientific information about the effects of pollutants upon a specific use of water. The criteria, therefore, are defined as the acceptable levels of concentrations of pollutants for a particular use and describe the water quality requirements for protecting aquatic biota and maintaining an individual water use e.g. drinking, bathing, irrigation, industrial etc. Various international and national agencies have defined water quality criteria for different uses of water in tropical/non-tropical regions e.g. European Community (EC) standards have been developed specifying the Guide Level and Maximum Admissible Level of pollutant concentration for three different uses of water vis-a-vis drinking, bathing and fish water. WHO standards are defined in terms of a Action Level, whereas, WQIHS, Teharan have defined standards as Acceptable Concentrations and Maximum Allowable Concentrations. In India, CPCB has defined five classes A to E specifying different levels of treatment required to these class of water for different uses such as drinking outdoor bathing, propogation of wildlife and fisheries, and irrigation and industrial cooling. Mostly the water quality parameters considered in defining these standards are pH, Temperature, Turbidity chlorides, SO4 NO3, BOD, DO, TDS, coliform and some of the important heavy metals. However, many other parameters are also considered by the individual agencies. Thus, it is seen that different agencies use different terminology for classification such as Guide Level, Action Level, Maximum Allowable Concentration and Acceptable Level etc. for defining the water quality criteria. Hence, it was felt that a common classification such as Excellent, Acceptable, Slightly Polluted, Polluted and Heavily Polluted water, is essential to know the water quality status. In this context, an attempt is made to define a common platform of water quality classification as given above considering the important indicator parameters and the standards suitable for Indian scenario. The CPCB criteria for different parameters has been given due consideration while defining the concentration levels in the newly defined classes. The parameters/classes for which criteria were not defined in CPCB standards, reference was made to the standards defined by other agencies. To each one of these classes integer values was assigned in geometric progression which indicate the level of pollution in numeric terms. These values were termed as class indices and form the basis for comparison of water quality from Excellent to heavily polluted. The mathematical expressions were fitted to concentration ranges/levels in each of these classes against the class index. Thus, given a set of observations on water quality in terms of the parameters considered in this work, the mathematical expressions for that parameter gives a numerical value indicating the status of water quality Excellent, Acceptable, Slightly Polluted, Polluted or Heavily Polluted water.