Iranian Water Quality Index (IWQI)
The aggregation of indices that represents the integrated effects of individual concentration of water quality parameters was proposed (Brown 1970) using the Delphi technique as a tool in a formal assessment procedure. Some scholars have considered different approaches. For example, Prati et al. (1971) considered 13 different parameters of equal weight in their system. The mathematical expression generally known as Water Quality Index was developed at the National Sanitation Foundation (NSF) during 1970s. It seems that the NSF’s work is the most comprehensive one that has been carried out to date and has been discussed in various papers (Brown et al. 1972; Landwehr & Deininger 1976). It is a weighted linear system of the sub-indices or a weighted product aggregation function. The WQI system is to assess water quality trends for management purposes even though it is not an absolute measure of degree of pollution or the actual water quality (Chai 1999). This classification technique may cause a rough and imprecise approach on data. Because some parameters are close to or far from the limit, they may have equal importance for evaluation of concentration (Yilmaz 2007). Conceptually, similar methods have been used in other countries for defining water quality. The Catalan Water Agency (Catalonia, Spain) uses 150 chemical indicators to investigate the condition of water. One of the obstacles that environmental managers are facing is how to transfer their interpretation of complex environmental data into the information that is understandable and useful to technical and policy related officials, as well as the general public. This is particularly important in reporting the condition of the environment. Internationally, there are numerous attempts to develop a method that could be able to meaningfully integrate the data sets and convert them into efficient information Nagels et al. 2001). Conventional water quality regulations contain quality classes which make the use of crisp sets of data. In addition, borders of different classes suffer inherent imprecision (Silvert 2000).
In Iran, the classification of rivers by the Iranian Department of Environment (IR-DOE) is generally carried out based on the National Sanitation Foundation Water Quality Index (NSFWQI). It should be pointed out that the sources of pollution may differ from place to place. Therefore, type of pollution and their impact on water quality should be taken into consideration while developing an index to access the water quality. For instance, many Iranian rivers receive larger amounts of coliforms due to fact that municipal sewage is not being efficiently treated before discharge into the environment.
Uses and Limitation:
The proposed water quality classification scheme and some other existing indices were applied to assess the water quality status at Karoon River which plays an important role as a source of water, biodiversity, tourist areas and place of living for local inhabitants. Since the ancient times, many important civilizations have risen in the regions, which could not come into existence in the first place without living in harmony with nature as well as practicing efficient use of limited resources in the area. Karoon River is also the main drinking water source for the many cities of Khozestan province in Iran, the water quality data of the unique observation site on the river were considered for estimation of IWQI. These data are available on Iranian Water Resources Management Company (WRMC). The subset of the data included 22 parameters for indices calculation. Some components like NH4 or Chl-a are missing on the limitations of the available dataset.
In the second step sub-index values were calculated using mathematical expressions that were given in Table 3 to assign a value of between 0 and 100 to each parameter. To compute the sub-indices, the characteristic value was accepted as 90th percentile of data set for each parameter. In the last step, a weighted sum method was employed to obtain overall index values using weights which are given in Table 2. The water quality for Karoon River at the Shatit Station (Pilot Station) has been assessed with the IWQ index. Data sets (1999–2000) from Iranian Department of Environment were used to assess water quality.
This index is useful for regions or countries that those classifications of water quality criteria are the same as Table 2, and with considering the limited number of parameters that traditionally placed in the analysis in some countries, meanwhile the IWQI involves some special number of parameters; we recommended that the IWQI may be applied to other regions.
Categorization Table
Table 1. IWQI categorization scheme
Standards Required
No water quality standard is required for calculations process of this index.
Variables Selection
Based on expert opinions and international experiences, six water quality parameters including DO, turbidity, pH, TDS, nitrate, and fecal coliform were considered as the significant indicator parameters of IWQI to assess the quality of surface water sources.
Calculation of Iranian Water Quality Index:
The organic pollution index (OPI) is represented in the following equation:
\begin{eqnarray*}
IWQI= \sum_{i=1}^{n} \ {W_{i}I_{i}}
\end{eqnarray*}
where Wi, weight for ith parameter (Table 2, mean value will be considered) and Ii, sub-index for ith parameter (symbolizes with ‘y’ of Table 3).
Table 2. Weighing factors
Table 3. Mathematical equaations formulated for IWQI
Case Studies based on Iranian Water Quality Index
a new index called the Iranian Water Quality Index was evaluated. It provides a simple representation of the extensive and complex variables (physical, biological and chemical) that govern the overall quality of surface water that is intended for potable use. Based on expert opinions and international experiences, six water quality parameters including DO, turbidity, pH, TDS, nitrate, and fecal coliform were considered as the significant indicator parameters of IWQI to assess the quality of surface water sources. The application of the new index was demonstrated at a sampling station on Karoon River in Iran, based on observed water quality data.
Water quality index is the flexible tool to develop classification model with a simple framework and constructed with natural language. In this study, water quality index value was obtained to express the classification of river in order to make water quality assessment more understandable especially in public consideration. We have assessed water quality in the Karoon River with physicochemical determinants. IWQI has demonstrated that water quality is high sustainable expected results in the Karoon River. The new index is believed to assist decision makers in reporting the condition of water quality and investigation of spatial and temporal changes in the river. In addition, it is useful to determine the level of capability for the individual parameter by referring to the concentration ranges defined in the proposed classification scheme. This index is useful for regions or countries that those classifications of water quality criteria are the same as Table 2, and with considering the limited number of parameters that traditionally placed in the analysis in some countries, meanwhile the IWQI involves some special number of parameters; we recommended that the IWQI may be applied to other regions.
References
F. Babaei Semiromi, A. H. Hassani, A. Torabian, A. R. Karbassi, F. Hosseinzadeh Lotfi; Evolution of a new surface water quality index for Karoon catchment in Iran. Water Sci Technol 1 December 2011; 64 (12): 2483–2491. doi: https://doi.org/10.2166/wst.2011.780