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 Table of Contents  
Year : 2015  |  Volume : 59  |  Issue : 2  |  Page : 153-155  

Application of water quality index for the assessment of suitability of natural sources of water for drinking in rural areas of east Sikkim, India

1 Ph.D Scholar, Department of Microbiology, Sikkim Manipal University, Gangtok, Sikkim, India
2 Professor and Head, Department of Microbiology, Sikkim Manipal University, Gangtok, Sikkim, India
3 Associate Professor, Department of Microbiology, Sikkim Manipal University, Gangtok, Sikkim, India

Date of Web Publication25-May-2015

Correspondence Address:
T Shantikumar Singh
Department of Microbiology, Sikkim Manipal Institute of Medical Sciences, Sikkim Manipal University, Gangtok, Sikkim
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0019-557X.157539

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In Sikkim, especially in the rural areas where there is no supply of treated water for drinking and other domestic uses, natural surface water is the only source. The objective was to assess the water quality of natural sources of water in the rural areas of East Sikkim using a water quality index (WQI) for different seasons. A total of 225 samples, that is, 75 in winter, 75 in summer, and 75 in monsoon were collected from different sources for physicochemical analysis, and a WQI was calculated. The water quality values ranged 32.01-96.71. The results showed that most of the water samples were in poor condition (85.3%) and very few of them were in good condition (2.6%). The water quality of the natural sources indicated that the water is poor-quality and not totally safe for human consumption, and that it needs treatment before consumption.

Keywords: Natural sources of water, physicochemical parameters, water quality index (WQI)

How to cite this article:
Poonia S, Singh T S, Tsering DC. Application of water quality index for the assessment of suitability of natural sources of water for drinking in rural areas of east Sikkim, India. Indian J Public Health 2015;59:153-5

How to cite this URL:
Poonia S, Singh T S, Tsering DC. Application of water quality index for the assessment of suitability of natural sources of water for drinking in rural areas of east Sikkim, India. Indian J Public Health [serial online] 2015 [cited 2022 Aug 20];59:153-5. Available from:

Water is one of the most vital natural resources for all life on Earth. The availability and quality of water have always played an important part in determining not only where people can live, but also their quality of life. It is therefore necessary that the quality of drinking water is checked at regular time intervals, because the human population can suffer from a variety of waterborne diseases due to contaminated drinking water.

Sikkim is a landlocked Indian state located in the Himalayan mountains, covering approx. 2,740 sq. m. East Sikkim district covers about 14% of its total area and has the highest population growth (15.73%) out of the four districts of Sikkim, with 46% of the state's total population residing there. Of this population, 56.81% live in the rural areas of the district. [1] The people in the rural areas depend on untreated surface water resources.

The water quality index (WQI) is an effective tool to monitor water pollution. It is a dimensionless number that combines multiple water quality factors into a single number and helps in interpreting the quality of water with a single numerical value. [2] The objective of the present study was to provide information on the physicochemical characteristics of the water sources of the rural areas of East Sikkim in order to assess the suitability of the water for human consumption based on computed WQI.

A total of 225 water samples, that is, 75 each in winter, summer, and monsoon were collected during the period from November 2011 to October 2012 from 75 villages. For the study, 30% of the villages of the district were taken into account, thus 75 villages were selected out of a total of 251 villages. A sample of 500 mL of water was collected from each site in plastic cans and analyzed for nine physicochemical parameters. The parameters color, odor, pH, temperature, turbidity, total dissolved solids (TDS), and dissolved oxygen (DO) were monitored at the sampling site, and the parameters total hardness and chloride were analyzed in the laboratory as per the standard methods of the American Public Health Association (APHA, 1995). [3] The WQI was calculated by using the standards of drinking water quality recommended by the Bureau of Indian Standards (BIS, 2003) and the Indian Council of Medical Research (ICMR, 1975). [4],[5] The weighted arithmetic index method was used for the calculation of the WQI. [6]

A WQI is calculated from the point of view of the suitability of water for human consumption. The "standards" and "unit weights" of the parameters measured for the drinking water recommended by the ICMR and the BIS are given in [Table 1].
Table 1: Drinking water standards with unit weights recommended by ICMR/BIS*

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The quality rating q n for the nth water quality parameter was obtained from the following relation:

where V n = estimated value of the nth parameter at a given sampling site, S n = standard permissible value of the nth parameter, and V io = ideal value of the nth parameter in pure water. All the ideal values (V io ) were taken as zero for drinking water except for pH = 7 and DO = 14.6 mg/L.

The unit weight (W n ) calculated for various water quality parameters is inversely proportional to the recommended standards for the corresponding parameters, as in the following:

where W n = unit weight for the nth parameters, S n = standard value for the nth parameters, and K=constant for proportionality.

The WQI was calculated from the following equation:

WQI = Σq n wnw n

Water quality can be categorized into five classifications, as excellent, good, poor, very poor, and unsuitable for drinking if the WQI value lies in the ranges of 0-25, 26-50, 51-75, 76-100, and above 100, respectively. [7]

The data were processed using the Statistical Package for Social Sciences (SPSS Inc. Released 2007, SPSS for Windows, Version 16.0. Chicago, SPSS Inc.).

The WQI for the water samples ranged 32.01-98.4. [Table 2] shows the WQI for the sampling sites in different seasons. Of the sampling sites, 76% were in the "poor" category in summer, followed by 70.6% in monsoon and 60% in winter; 34.6% of water samples were in the "good" category in winter and 25.3% were of "very poor" quality in monsoon. None of the samples were in the "excellent" or "unsuitable for drinking" categories. Water quality was better in winter compared to that in summer or monsoon [Table 2].
Table 2: Water quality index (WQI) values of sampling sites in different seasons as found in the study

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The water samples were found to be colorless and odorless. The average temperature ranged 3-26°C, with mean values 7.68 ± 2.18 in winter, 18.9 ± 3.87 in summer, and 15.16 ± 3.72 in monsoon. The pH ranged 5.5-7.5, with mean values 6.52 ± 0.39 in winter, 6.56 ± 0.33 in summer, and 6.36 ± 0.35 in monsoon. The pH was observed to decline during the monsoon and increase in the winter season. The range of turbidity in the study varied 2-25 NTU, with mean values 4.69 ± 1.91 in winter, 13.20 ± 4.98 in summer, and 15.76 ± 3.72 in monsoon. TDS in the studied area varied in the range of 20-135 mg/L, with mean values 50.83 ± 21.35 in winter, 61.81 ± 21.31 in summer, and 62.81 ± 22.24 in monsoon. In the study, values of hardness fluctuated in the range of 48-129 mg/L, with mean values 99.92 ± 17.22 in winter, 83.76 ± 14.72 in summer, and 70.37 ± 12.24 in monsoon. The chloride concentration fluctuated in the range of 10-44 mg/L, with mean values 18.31 ± 5.27 in winter, 29.35 ± 6.79 in summer, and 23.44 ± 6.24 in monsoon. DO varied in the range of 3.1-9.8 mg/L, with mean values 8.02 ± 1.38 in winter, 6.13 ± 1.09 in summer, and 6.72 ± 1.42 in monsoon. All the parameters in all seasons differed statistically (P < 0.01) from the standard values.

The water was found to be more turbid during the monsoon and summer seasons than during the winter season. This can be caused by soil erosion, water discharge, agricultural runoff, etc. Similarly, other authors in their studies reported high turbidity in summer and monsoon compared to winter. [8] Turbidity was within the permissible limits only in the winter season. TDS values in the studied area were within the permissible limits. The average value of TDS was found to be higher in summer than in winter. Several other studies showed similar observations of TDS being high in summer. [8],[9] Hardness was found to be well within the permissible limits. The hardness was found to be the highest in winter, followed by summer and monsoon.

Chloride was within the permissible limits. Seasonally, chloride was found to be high in summer, followed by monsoon and winter. Similar observations have been made by several authors. [8],[10] Seasonally, the concentration of DO was the highest during winter, followed by monsoon and summer. This observation is in conformity with the observations of some other studies. [10],[11] In contrast to our study, some authors observed high concentrations of DO during the summer. [8]

The mean values of WQI for all the sampling sites in the different seasons, that is, winter, summer, and monsoon are 55.17 ± 9.98, 66.77 ± 10.34, and 68.29 ± 11.5 respectively, which indicates poor quality of water. [7] Most of the samples, that is, 76% showed poor quality of water in summer. Several other studies based on WQI for untreated natural water conducted in India have also reported poor quality of water in summer and monsoon compared to the winter season. [9],[10]

In this study, the overall quality of water was assessed by applying a WQI. WQI has some limitations-it may not carry enough information about the actual situation of the water bodies, with the aggregation of data perhaps masking short-term water quality problems. However, the WQI method more than compensates for such drawbacks. This method is more systematic and enables the comparative evaluation of water quality of multiple sampling sites. In this study, WQI values revealed that the present status of water quality is not suitable for drinking purposes, and therefore water should be treated properly before use. It is recommended that more surveys be conducted covering more areas, to develop water treatment and purification plants in specific locations, and to propagate public health education. The results of this study are expected to be a helpful tool for the public and for water quality management.

   References Top

Census of India 2011 provisional, Directorate of Census, Sikkim, India. Available from: [Last accessed on 2014 Jan 1].  Back to cited text no. 1
Horton RK. An index number for rating water quality. J Water Pollut Control Fed 1965;37:300-5.  Back to cited text no. 2
American Public Health Association (APHA). Standard Methods for the Examination of Water and Waste Water. 19 th ed. Washington DC: American Public Health Association; 1995.  Back to cited text no. 3
BIS. Indian Standards Specifications for Drinking Water IS: 10500. New Delhi: Bureau of Indian Standards; 2003.  Back to cited text no. 4
Indian Council of Medical Research (ICMR). Manual of Standards of Quality for Drinking Water Supplies. Special Report Series No. 44. New Delhi: Indian Council of Medical Research; 1975.  Back to cited text no. 5
Brown RM, McClelland NI, Deininger RA, O'Connor MF. A water quality index - crasing the psychological barrier. Proceedings of the 6 th Annual Conference. Adv Water Pollut Res 1972;6:787-94.  Back to cited text no. 6
Chatterjee AA. Water quality of Nandankanan Lake, India. J Environ Health 1992;34:329-33.  Back to cited text no. 7
Manjare SA, Vhanalakar SA, Muley DV. Analysis of water quality using physico-chemical parameters, Tamdalge tank in Kohlapur District, Maharashtra. Int J Adv Biotechnol Res 2010;1:115-9.  Back to cited text no. 8
Thakor FJ, Bhoi DK, Dabhi HR, Pandya SN, Chauhan NB. Water quality index of Pariyej lake dist. Kheda-Gujrat. Curr World Environ 2011;6:225-31.  Back to cited text no. 9
Kotadiya NG, Acharya C, Radadia BB, Solanki HA. Determination of water quality index and suitability of a rural freshwater body in Ghuma village, District Ahmedabad, Gujrat. Life Sci Leafl 2013;2:68-75.   Back to cited text no. 10
Pejman AH, Bidhendi GR, Karbassi AR, Mehrdadi N, Bidhendi EM. Evaluation of spatial and seasonal variations in surface water quality using multivariate statistical techniques. Int J Environ Sci Tech 2009;6:467-76.  Back to cited text no. 11


  [Table 1], [Table 2]

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