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Water Quality Index
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A critical water quality index (WQI) method has been used to determine the overall water quality status of surface water and groundwater systems globally since the 1960s. WQI follows four steps: parameter selection, sub-indices, establishing weights, and final index aggregation.

  • water quality assessment
  • physicochemical and biological parameters
  • water quality index
  • multi-criteria decision-making
  • analytical hierarchical process

1. Introduction

Water quality is intrinsically connected to human health, food production, gender equality, reduction of poverty, ecosystem livelihoods, economic development, and social growth in our communities [1]. It is also one of the major problems in water resource planning and management. Furthermore, an increase in urbanization, construction, agricultural activities, industrial applications, and natural processes has adversely impacted the quality of surface water and groundwater, and its effects on human health throughout the world, as shown in Figure 1 [2]. Water quality is usually classified into biological, physical, and chemical parameters, and there are several parameters for each category [3]. The evaluation of these three categories, based on parameters through field monitoring of water sampling, provides essential information for identifying trends, a wider range of knowledge to water resource authorities, and future planning recommendations [4]. Water quality analysis typically relates to the quality of natural water and its possible uses (drinking, domestic, irrigation, and industries). In reality, it is expensive and laborious to monitor the parameters of multiple contamination sources entering into surface water bodies and groundwater systems. Furthermore, numerous researchers and scientists have faced difficulties in describing and addressing water in a consolidated and simple way [5]. These difficulties happen because of the complexity of water quality parameters and the wide variability in parameters utilized for characterizing the status of water quality of water resources. This has contributed to several comprehensive efforts, without losing its scientific basis, to define the water quality status in simple ways [6].

Figure 1. Shows the quality of surface water and groundwater resources degrading by anthropogenic and natural processes from various sources, as well as the effect on human health through these activities.

Regardless of this development, a simple evaluation of the water quality of groundwater and surface water is challenging to determine. The combined impact of many different factors that characterize the water quality and the challenges of classifying the significant parameters used to measure the status of water resources quantitatively are very complex to understand. Therefore, the water quality index (WQI) is considered a mathematical tool that significantly minimizes the complex water quality data sets and provides a single classifying value that describes the water quality status of water bodies or degree of pollution. Furthermore, WQI is a single dimensionless number that describes the overview of the overall water quality status in a simple way by aggregating the measurements of selected parameters such as pH, nitrate, dissolved oxygen (DO), heavy metal. [7]. As early as 1965, this method was introduced through mathematical equations to determine water quality status in the river by Horton [8]. The WQI is determined based on various biological, physical, and chemical parameters that define the various purposes of utilization of water bodies for human consumption, such as recreation, drinking, industries, irrigation, and domestic. After the proposed WQI method by Horton, the numbers of WQI methods have been developed for various purposes by numerous organizations across the globe, such as the National Sanitation Foundation Water Quality Index (NSFWQI) [9], Scottish Research Development Department (SRDD) [10], River Status Index (RSI) [11], Canadian Council of Ministers of the Environment Water Quality Index (CCMEWQI) [12], British Columbia Water Quality Index (BCWQI) [13], Overall Index of Pollution (OIP) [14], Oregon Water Quality Index (OWQI) [15], Bhargava Method Water Quality Index (BMWQI) [16], Malaysia Water Quality Index (MWQI) [17], Water Contamination Index (WCI) [18], Vaal Water Quality Index (Vaal WQI) [19], etc.

Moreover, four common steps have been used in the WQI method, including the parameters selection, sub-indices establishment, assigning of weights (equally or unequally), and aggregation of sub-indices to obtain the final index [4]. Previous studies have shown that most researchers have applied all steps (because they used unequal weights, such as NSFWQI, SRDD, MWQI, etc.). Some of them used three steps (equal weights, such as OIP, WCI, RSI, etc.), but few of them reported that they directly used the formula for water quality assessment (CCMEWQI) [20]. Furthermore, the WQI method has been applied for different purposes, but mainly for surface water quality (especially for river water) [21][22][23][24][25][26][27][28][29], groundwater quality [1][30][31][32][33][34][35][36], and wetland [37][38][39][40][41][42] across the world. Moreover, the Environmental Protection Agency (EPA) of the Republic of Serbia also utilizes WQI to inform about the overall status of the river water system [43]. In this technique, a large resource of water is easily accessed for water quality assessment because of the consistent scale using the WQI equation. Multiple parameters are used to calculate in a single number and the flexibility of selecting the characteristics of water quality. However, the calculation of WQI is a prolonged process in which numerous national and international standards are taken into consideration, in terms of criteria of water consumption. This makes the process more complicated, despite having simple calculations. Moreover, it is easy to bias the process of selecting parameters and calculating the individual weighting values. Therefore, the covered parameters cannot be definite in number that they would give a simple WQI; it may not be enough to understand, as a whole, the WQI of a large water body because certain parameters can influence the water quality in a wider manner, which can be neglected during the calculation.

The literature reviewed indicates that all of the indices have their limitations and strengths; therefore, many organizations and agencies do not consider this methodology for developing a WQI worldwide [7][44]. However, it is pertinent to mention that the strengths and weaknesses of the processes in establishing WQI for water quality assessment can be simplified by multi-criteria decision-making (MCDM) approaches to evaluate the parameter’s weight separately. In previous years, analytical techniques have significantly increased to resolve the problems related to water resources, where MCDM procedures are generally regarded as very effective in addressing water management problems [45]. The effectiveness of such procedures depends on the conceptual framework of assessment processes and on the common language used to identify and address complex water challenges. Moreover, MCDM easily allows—in the process of decision-making—the impact of uncertainties that often define water management problems [46]. In previous decades, several authors have applied the MCDM method to various purposes in water resource management, assessment of water quality [46][47] as well as in other areas, to solve problems surrounding the environment, energy, and sustainability [48], safety and risk management [49], and technology and information management [50]. There are numerous MCDM approaches available for solving problems related to water resources, such as analytical network process (ANP), analytical hierarchical process (AHP), data envelopment analysis (DEA), fuzzy decision-making (FDM), measuring attractiveness by a categorically based evaluation technique (MACBETH), simple additive weighting (SAW), supply chain management (SCM), a technique for order preference by similarity to ideal solution (TOPSIS), compromise programming (CP), etc. [51][52][53][54][55].

2. Importance of WQI

In general, WQI is the comparison of the amount with an arbitrary or scientific standard or with a pre-specified base. Therefore, the WQI monitored and reported environmental status and trends on standards quantitatively. The WQI method provides effective information on the degree of purity and pollution of water, by avoiding an overwhelming quantity of data to demonstrate water quality [56]. The WQI tool also facilitates a perfect quality monitoring system accessible. The monitoring data should formulate easy to comprehend indices to executive management and the overall development of public policies to accomplish this. The National Academy of Sciences (NAS)’s Planning Committee on Environmental Indices [57], found that environmental indicators play an active role in assisting with program design, assigning policy details, and communicating facilitation with affected individuals.

Ott [58] identified the following six basic usages of WQI after examining relevant literature available on the subject: resource assignment, standard enforcement, trend analysis, location ranking, public information, and scientific research. This means that indices are descriptive and objective methods for evaluating water quality trends. Parameters are not concisely graphical against one another, or against time, and do not explicitly indicate the patterns due to overlap in data and volume.

  • Scientific research: indices can be used to minimize a large number of data into a process that provide insight into research and perform an analysis of many of these environmental programs.

  • Public information: indices can be applied to educate the public on environmental conditions.

  • Trend analysis: indices can be utilized for environmental information, at various time periods, to evaluate changes in environmental quality that have taken place over the period.

  • Standard enforcement: indices can be applied to particular areas to evaluate the extent to which legislature standards and existing criteria are fulfilled or exceeded.

  • Resource assignment: the location ranking, by evaluating the environmental conditions at various places or geographical regions.

Almost every WQI relies on normalization, the data parameter-by-parameter, as per the predicted concentration levels, and the interpretation of “bad” versus “good” levels. After this, index is calculated as a weighted average for all observed values, with weighted parameters according to their perceived significance to overall water quality. The purposes of the WQI method are, particularly, for the evaluation of the overall status of water quality (parameters of physical, biological, and chemical) and the use of water resources for multiple purposes. WQI methods were developed by individuals, organizations, and agencies, and classified into four groups (discussed below):

  • Specific indices: the water classification in this category is based on the type of use and requirement (drinking, irrigation, industries, bathing, etc.), which is defined by OWQI, CCME, etc.

  • Public indices: the type of water used in the assessment process, such as NSFWQI, (Horton 1965), are ignored in this category.

  • Statistical indices: the statistical approaches are used in these indices and personal opinions are not included.

  • Planning indices: this step includes an instrument tool that facilitates decision-making and makes a plan for managing water quality projects.


  1. Jha, M.K.; Shekhar, A.; Jenifer, M.A. Assessing Groundwater Quality for Drinking Water Supply Using Hybrid Fuzzy-GIS-Based Water Quality Index. Water Res. 2020, 179, 1–16.
  2. Akhtar, N.; Syakir, M.I.; Rai, S.P.; Saini, R.; Pant, N.; Anees, M.T.; Qadir, A.; Khan, U. Multivariate Investigation of Heavy Metals in the Groundwater for Irrigation and Drinking in Garautha Tehsil, Jhansi District, India. Anal. Lett. 2020, 53, 774–794.
  3. Akhtar, N.; Syakir, M.I.; Anees, M.T.; Qadir, A.; Yusuff, M.S. Characteristics and Assessment of Groundwater. In Groundwater; Chapter 3; IntechOpen: London, UK, 2020; pp. 1–20.
  4. Sutadian, A.D.; Muttil, N.; Yilmaz, A.; Perera, C. Development of River Water Quality Indices—A Review. Environ. Monit. Assess. 2016, 188, 1–33.
  5. Lumb, A.; Sharma, T.C.; Bibeault, J.F. A Review of Genesis and Evolution of Water Quality Index (WQI) and Some Future Directions. Water Qual. Expo. Health 2011, 3, 11–24.
  6. Banda, T.D.; Kumarasamy, M. A Review of the Existing Water Quality Indices (WQIs). J. Phys. Opt. 2020, 2, 1–19.
  7. Abbasi, T.; Abbasi, S.A. Water Quality Indices; Elsevier: Amsterdam, The Netherlands, 2012.
  8. Horton, R.K. An Index Number System for Rating Water Quality. J. Water Pollut. Control Fed. 1965, 37, 300–306.
  9. Brown, R.M.; McClelland, N.I.; Deininger, R.A.; Tozer, R.G. A Water Quality Index—Do We Dare? Water Sew. Works 1970, 117, 339–343.
  10. Scottish Research Development Department (SRDD). Development of a Water Quality Index; Engineering Division: Edinburg, UK, 1976.
  11. Liou, S.M.; Lo, S.L.; Wang, S.H. A Generalized Water Quality Index for Taiwan. Environ. Monit. Assess. 2004, 96, 35–52.
  12. Canadian Council of Ministers of the Environment (CCME). Canadian Water Quality Index 1.0 Technical Report and User’s Manual; Canadian Environmental Quality Guidelines Water Quality Index Technical Subcommittee: Gatineau, QC, Canada, 2001.
  13. Zandbergen, P.A.; Hall, K.J. Analysis of the British Columbia Water Quality Index for Watershed Managers: A Case Study of Two Small Watersheds. Water Qual. Res. J. 1998, 33, 519–549.
  14. Sargaonkar, A.; Deshpande, V. Development of an Overall Index of Pollution for Surface Water Based on a General Classification Scheme in Indian Context. Environ. Monit. Assess. 2003, 89, 43–67.
  15. Cude, C.G. Oregon Water Quality Index a Tool for Evaluating Water Quality Management Effectiveness. J. Am. Water Resour. Assoc. 2001, 37, 125–137.
  16. Bhargave, D.S. Expression for Drinking Water Supply Standards. J. Environ. Eng. 1985, 111, 304–310.
  17. Shuhaimi-Othman, M.; Lim, E.C.; Mushrifah, I. Water Quality Changes in Chini Lake, Pahang, West Malaysia. Environ. Monit. Assess. 2007, 131, 279–292.
  18. Nemerow, N.L. Benefits of Water Quality Enhancement; Environmental Protection Agency, Water Quality Office, US Government: Washington, DC, USA, 1971.
  19. Banda, T.D. Developing an Equitable Raw Water Pricing Model: The Vaal Case Study. Master’s Thesis, Tshwane University of Technology, Pretoria, South Africa, 2015.
  20. Banda, T.D.; Kumarasamy, M. Aggregation Techniques Applied in Water Quality Indices (WQIs). Pollut. Res. 2020, 39, 400–441.
  21. Qu, X.; Chen, Y.; Liu, H.; Xia, W.; Lu, Y.; Gang, D.D.; Lin, L.S. A Holistic Assessment of Water Quality Condition and Spatiotemporal Patterns in Impounded Lakes along the Eastern Route of China’s South-to-North Water Diversion Project. Water Res. 2020, 185, 1–14.
  22. Ma, Z.; Li, H.; Ye, Z.; Wen, J.; Hu, Y.; Liu, Y. Application of Modified Water Quality Index (WQI) in the Assessment of Coastal Water Quality in Main Aquaculture Areas of Dalian, China. Mar. Pollut. Bull. 2020, 157, 1–18.
  23. Nong, X.; Shao, D.; Zhong, H.; Liang, J. Evaluation of Water Quality in the South-to-North Water Diversion Project of China Using the Water Quality Index (WQI) Method. Water Res. 2020, 178, 1–15.
  24. Şener, Ş.; Şener, E.; Davraz, A. Evaluation of Water Quality Using Water Quality Index (WQI) Method and GIS in Aksu River (SW-Turkey). Sci. Total Environ. 2017, 584–585, 131–144.
  25. Hurley, T.; Sadiq, R.; Mazumder, A. Adaptation and Evaluation of the Canadian Council of Ministers of the Environment Water Quality Index (CCME WQI) for Use as an Effective Tool to Characterize Drinking Source Water Quality. Water Res. 2012, 46, 3544–3552.
  26. Wu, Z.; Wang, X.; Chen, Y.; Cai, Y.; Deng, J. Assessing River Water Quality Using Water Quality Index in Lake Taihu Basin, China. Sci. Total Environ. 2018, 612, 914–922.
  27. Effendi, H.; Romanto; Wardiatno, Y. Water Quality Status of Ciambulawung River, Banten Province, Based on Pollution Index and NSF-WQI. Procedia Environ. Sci. 2015, 24, 228–237.
  28. De Oliveira, M.D.; de Rezende, O.L.T.; de Fonseca, J.F.R.; Libânio, M. Evaluating the Surface Water Quality Index Fuzzy and Its Influence on Water Treatment. J. Water Process. Eng. 2019, 32, 100890.
  29. Ghimire, S.; Flury, M.; Scheenstra, E.J.; Miles, C.A. Spatio-Temporal Variation of WQI, Scaling and Corrosion Indices, and Principal Component Analysis in Rural Areas of Marand, Iran. Sci. Total Environ. 2019, 11, 1–09.
  30. Seifi, A.; Dehghani, M.; Singh, V.P. Uncertainty Analysis of Water Quality Index (WQI) for Groundwater Quality Evaluation: Application of Monte-Carlo Method for Weight Allocation. Ecol. Indic. 2020, 117, 106653.
  31. Sahoo, S.; Khaoash, S. Impact Assessment of Coal Mining on Groundwater Chemistry and Its Quality from Brajrajnagar Coal Mining Area Using Indexing Models. J. Geochem. Explor. 2020, 215, 1–17.
  32. Adimalla, N.; Qian, H. Groundwater Quality Evaluation Using Water Quality Index (WQI) for Drinking Purposes and Human Health Risk (HHR) Assessment in an Agricultural Region of Nanganur, South India. Ecotoxicol. Environ. Saf. 2019, 176, 153–161.
  33. Yousefi, H.; Zahedi, S.; Niksokhan, M.H. Modifying the Analysis Made by Water Quality Index Using Multi-Criteria Decision Making Methods. J. Afr. Earth Sci. 2018, 138, 309–318.
  34. Sutadian, A.D.; Muttil, N.; Yilmaz, A.G.; Perera, B.J.C. Using the Analytic Hierarchy Process to Identify Parameter Weights for Developing a Water Quality Index. Ecol. Indic. 2017, 75, 220–233.
  35. Yan, F.; Qiao, D.; Qian, B.; Ma, L.; Xing, X.; Zhang, Y.; Wang, X. Improvement of CCME WQI Using Grey Relational Method. J. Hydrol. 2016, 543, 316–323.
  36. Mohebbi, M.R.; Saeedi, R.; Montazeri, A.; Vaghefi, K.A.; Labbafi, S.; Oktaie, S.; Abtahi, M.; Mohagheghian, A. Assessment of Water Quality in Groundwater Resources of Iran Using a Modified Drinking Water Quality Index (DWQI). Ecol. Indic. 2013, 30, 28–34.
  37. Fathi, P.; Ebrahimi, E.; Mirghafarry, M.; Esmaeili Ofogh, A. Water Quality Assessment in Choghakhor Wetland Using Water Quality Index (WQI). Iran. J. Fish. Sci. 2016, 15, 508–523.
  38. Bassi, N.; Kumar, M.D. Water Quality Index as a Tool for Wetland Restoration. Water Policy. 2017, 19, 390–403.
  39. Al-Musawi, N.O.; Al-Obaidi, S.K.; Al-Rubaie, F.M. Evaluating Water Quality Index of Al Hammar Marsh, South of Iraq with the Application of GIS Technique. J. Eng. Sci. Technol. 2018, 13, 4118–4130.
  40. Singh, A.K.; Sathya, M.; Verma, S.; Jayakumar, S. Spatiotemporal Variation of Water Quality Index in Kanwar Wetland, Begusarai, India. Sustain. Water Resour. Manag. 2020, 6, 1–8.
  41. Hong, Z.; Zhao, Q.; Chang, J.; Peng, L.; Wang, S.; Hong, Y.; Liu, G.; Ding, S. Evaluation of Water Quality and Heavy Metals in Wetlands along the Yellow River in Henan Province. Sustainability 2020, 12, 1300.
  42. Ghorbani, A.; Mohammadi, M.; Mohammadi, Z. Water Quality Evaluation of Torghabeh River of Mashhad Using Combination of NSFWQI Index and Geographic Information System. Int. J. Adv. Biol. Biomed. Res. 2014, 2, 2416–2430.
  43. Mladenović-Ranisavljević, I.I.; Takić, L.; Nikolić, Đ. Water Quality Assessment Based on Combined Multi-Criteria Decision-Making Method with Index Method. Water Resour. Manag. 2018, 32, 2261–2276.
  44. Sarkar, K.; Majumder, M. Application of AHP-Based Water Quality Index for Quality Monitoring of Peri-Urban Watershed. Environ. Dev. Sustain. 2021, 23, 1780–1798.
  45. Chung, E.S.; Kim, S.U.; Park, K.S.; Lee, K.S. Integrated Watershed Management Using Multicriteria Decision Making Techniques; International Water Resources Association (IWRA): Cancun, Quintana Roo, Mexico, 2017; pp. 1–12.
  46. Jakeman, A.J.; Giupponi, C.; Karssenberg, D.; Hare, M.P.; Fassio, A.; Letcher, R.A. Integrated Management of Water Resources: Concepts, Approaches and Challenges. In Sustainable Management of Water Resources: An Integrated Approach; Edward Elgar: Northampton, MA, USA, 2006.
  47. Talukder, B.; Blay-Palmer, A.; Hipel, K.W.; VanLoon, G.W. Elimination Method of Multi-Criteria Decision Analysis (MCDA): A Simple Methodological Approach for Assessing Agricultural Sustainability. Sustainability 2017, 9, 287.
  48. Soltani, A.; Hewage, K.; Reza, B.; Sadiq, R. Multiple Stakeholders in Multi-Criteria Decision-Making in the Context of Municipal Solid Waste Management: A Review. Waste Manag. 2015, 35, 318–328.
  49. Oztaysi, B. A Decision Model for Information Technology Selection Using AHP Integrated TOPSIS-Grey: The Case of Content Management Systems. Knowl. Based Syst. 2014, 70, 44–54.
  50. Ilangkumaran, M.; Karthikeyan, M.; Ramachandran, T.; Boopathiraja, M.; Kirubakaran, B. Risk Analysis and Warning Rate of Hot Environment for Foundry Industry Using Hybrid MCDM Technique. Saf. Sci. 2014, 72, 133–143.
  51. Yilmaz, B.; Harmancioglu, N.B. Multi-Criteria Decision Making for Water Resource Management: A Case Study of the Gediz River Basin, Turkey. Water SA 2010, 36, 563–576.
  52. Alamanos, A.; Mylopoulos, N.; Loukas, A.; Gaitanaros, D. An Integrated Multicriteria Analysis Tool for Evaluating Water Resource Management Strategies. Water 2018, 10, 1795.
  53. Wang, H.; Cai, Y.; Tan, Q.; Zeng, Y. Evaluation of Groundwater Remediation Technologies Based on Fuzzy Multi-Criteria Decision Analysis Approaches. Water 2017, 9, 443.
  54. Chung, E.S.; Lee, K.S. Identification of Spatial Ranking of Hydrological Vulnerability Using Multi-Criteria Decision Making Techniques: Case Study of Korea. Water Resour. Manag. 2009, 23, 2395–2416.
  55. Ceballos, B.; Lamata, M.T.; Pelta, D.A. A Comparative Analysis of Multi-Criteria Decision-Making Methods. Prog. Artif. Intell. 2016, 5, 315–322.
  56. Bharti, N.; Katyal, D. Water Quality Indices Used for Surface Water Vulnerability Assessment. Int. J. Environ. Sci. 2011, 2, 154–173.
  57. Wendling, Z.A.; Emerson, J.W.; Esty, D.C.; Levy, M.A.; Sherbinin, A. Environmental Performance Index; Yale Center for Environmental Law & Policy, Yale University: New Haven, CT, USA, 2018; Available online: (accessed on 1 February 2021).
  58. Ott, W.R. Environmental Indices: Theory and Practice; Ann Arbor Science Publishers: Ann Arbor, MI, USA, 1978.
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    Akhtar, N. Water Quality Index. Encyclopedia. Available online: (accessed on 20 August 2022).
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    Akhtar, N. (2021, April 08). Water Quality Index. In Encyclopedia.
    Akhtar, Naseem. ''Water Quality Index.'' Encyclopedia. Web. 08 April, 2021.