Water Quality Index and Status

Abstract

This chapter includes a methodology for determining the water quality status of a river. The water quality of the Yamuna River is described using indirect and direct methods. The indirect method is based on various water quality indices (WQI), whereas the direct method uses water quality data at various locations on the river. Detailed mathematical formulations of the various WQIs, such as National Sanitation Foundation (NSF), Nonlinear NSF, Canadian Council method, Nasirian (2007) method, Universal method, and European Classification Scheme, are pre-sented. Besides the WQI-based approach, a detailed analysis of water quality data is presented in order to determine water quality trends, profile, and monthly variations in the river. The bio-mapping technique is also used to detect the gradual change in the water quality status of the Yamuna River. 11.1 Water Quality Index Continuous assessment of physical, chemical and biological parameters of water is an essential part of water quality control programmes. These efforts lead to the accumulation of considerable information which cannot usually produce direct qual-itative determination of water quality. Various methods of data manipulations have been used to condense these records into a more suitable form, and promote effec-tive communication to all concerned. Moreover, these methods can produce a proper means for classification and comparison of different water bodies. The water quality index (WQI) system is a well-known method of expressing water quality that offers a simple, stable and reproducible unit of measure which responds to changes in the principal characteristics of water (Brown et al., 1972). WQI can be defined as a single numerical expression which reflects the com-posite influence of significant physical, chemical and microbiological parameters of water quality. A number of indices have been developed to summarize water quality data in an easily expressible and easily understood format (Couillard and Lefebvre, 1985). Since Horton (1965) proposed the first WQI, a great deal of consideration has been given to the development of index methods. The basic differences among these indices are the way their sub-indices were developed. Walski and Parker (1974) used an exponential function to represents the sub indices of various qual-ity variables. Landwehr (1979) suggested the Pearson type 3-distribution function to represent the sub-indices of all quality variables. Bhargava (1987) modified the