C H A P T E R

16

Water-Quality Indices: Looking Back,Looking Ahead

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16.1. Introduction 35

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16.2. The Best WQI? 354

16.3. The Path Ahead 355

ater Quality Indices DOI: 10.1016/B978-0-444-54304-2.00016-6 353

16.4. The Last Word 35

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16.1. INTRODUCTION

It is about 160 years since the concept ofwater quality was advanced to categorise waterof different streams and lakes according to thedegree of purity/impurity of the water course(Lumb et al., 2011, citing Sladecek, 1973 andothers). The first modern water-quality index(WQI) e that of Horton (1965) e came about46 years ago. It heralded a new era because itpresented a simple mathematical procedurewhich integrated physical, chemical and(some) biological parameters into a single score.It was an approach which has influenced thedevelopment of all subsequent WQIs, predomi-nantly based on physico-chemical parameters.The first modern bioassessment-based WQI ethe ‘Trent Biotic Index’ (TBI) e was introducedjust a little before the Horton’s index (in 1964).

TBI (Abbasi and Abbasi 2011) was intendedfor the streams of Florida, USA. Sixteen yearslater, Karr (1981) was to present the first-ever‘index of biotic integrity’ (IBI) which was tostimulate, and continues to do so, enormoususeful work in bioassessment-based categorisa-tion of water quality. By a coincidence all thethree classes of WQIs were introduced by scien-tists working in the USA.

After the introduction of the TBE and theHorton’s index, the remaining 3½ decades ofthe 20th century witnessed a rapid growth inthe popularity of WQIs, especially in developedcountries. These WQIs were based on ‘crisp’and ‘deterministic’ mathematical treatment ofwater quality data or biological assemblageinformation and the advancements were aimedat enhancing the objectivity (in the choice ofrepresentative parameters and assignment of

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16. WATER-QUALITY INDICES: LOOKING BACK, LOOKING AHEAD354

weightage), sensitivity (to changes in waterquality), clarity (in showing a water source upas bad/fair/good/very good, etc), and reach(appropriateness for larger number of regionsand types of water use) of the indices. In thecourse of achieving these objectives, some ofthe shortcomings of the different indices cameto the fore especially the ones relating to theaggregation methods used for indices basedpredominantly on physico-chemical character-istics, and the sampling/scaling methods usedin the BIs and the IBIs.

A great deal of work was done in solving theproblems of ambiguity, eclipsing, rigidity, etc,faced by the WQIs. More and more techniquesof statistics were pressed into service to achievethis objective. Its most spectacular use was inthe development of the RIVPACS (River Pollu-tion Assessment and Classification System) inGreat Britain (Clarke et al., 2003).

As the world moved into the last decade ofthe 20th century, there was increasing realizationabout the fuzziness and stochasticity associatedwith the steps of sampling, analysis and demar-cation of water quality. It was increasingly real-ised that ‘crisp’ and deterministic approacheswere not able to capture the ground reality;the resulting index scores tended to give unreal-istically sharp cut-offs due to their inability to‘sense’ grey areas.

These concerns and the lead-up studies(Kung et al., 1992; Lu et al., 1999; Silvert, 1997;2000; Chang et al., 2001; Lu and Lo, 2002;Haiyan, 2002, and others) resulted in the firstfuzzy WQI (Ocampo-Duque et al., 2006) andthe first stochastic WQI (Beamonte et al., 2005).The increasing application of the concepts ofartificial intelligence in water resource systemsalso saw the first Al-based WQI e the one inwhich genetic algorithm was applied (Peng,2004). During the last 5 years, the applicationof fuzzy rules in WQI development has intensi-fied. Several other techniques and tools of Aland statistics are also being increasingly appliedto WQIs based on physico-chemical parameters.

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In the bioassessment-based methods, also, evergreater sophistication is being introduced.

16.2. THE BEST WQI?

Despite a plethora of indices which have beendeveloped, and used, across the world it is notpossible to say which index is the best or evenlist ‘ten best’ or ‘twenty best’ indices. One doesfind that some indices are more popular thansome others. For example, the US National Sani-tation Foundation’s WQI, which is commonlyreferred as NSF-WQI (Brown et al., 1970), isused not only in the country of its origin butalso in several other countries spanning severalcontinents (Brazil, Mexico, Guinea-Bissau,Poland, Egypt, Portugal, Italy and India, amongothers). The WQI of the Canadian Council ofMinisters of the Environment, called CCME-WQI (CCME, 2001), which has come 31 yearsafter NSF-WQI, is another index which is usedin many countries besides the country of itsorigin (Lumb et al., 2011). CCME-WQI has alsobeen shown to be an index particularly suitedfor use with continuous water-quality moni-toring networks (Torredo et al., 2010). An indexfor groundwater-quality assessment proposedby Tiwari and Mishra (1985) from India isanother WQI used extensively in many coun-tries. There are takers for the WQI of Bharagava(1985) outside India (Lumb et al., 2011).

While each index has its special virtues andshortcomings, no attempt has been made so farto quantitatively ‘weigh’ different indices andsuggest which pulls how much weight. Hence,it is not possible to say exactly why some indicesare more popular than some other. Fernandezet al. (2004) compared 36 WQIs to observe thatappreciable differences exist between classifica-tions given by different indices on the samewater sample. These differences arise primarilybecause of differing parameter types andnumbers, weightage assignments and aggrega-tion formulae on which different indices are

LOOKING AHEAD

16.4. THE LAST WORD 355

based. As WQIs have been developed indifferent geographic, regional and managementcontexts, and there is no procedure yet in placeto compare their performance, all one can do isto look at complementarities of the information,credibility of measurements, transparency inindice formulation, relevancy of key parametersselected and comparability of results, to makequalitative judgement on the suitability orotherwise of a WQI.

16.3. THE PATH AHEAD

The situation described in the precedingsection points towards a need to devise a proce-dure with which the performance of variousWQIs can be compared in terms of efficiency,adequacy, inexpensiveness, reach and flexi-bility. Enormous historical water-quality dataare lying archived in many countries; suchdata can be used in testing the efficacy ofdifferent WQIs and in developing a universalWQI (Lumb et al., 2011). The concept of‘virtual water-quality metre (VIRWQIM)’ intro-duced by Sarkar and Abbasi (2006) can comehandy in this initiative because, with it, virtual‘dash boards’ can be created wherein differentVIRWQIMs can show classification of a watersource as per different indices at a giventime, besides providing an integrated, overall,assessment.

Besides increasing use of Al, advanced statis-tics and probability theory, the field of WQI hasalso witnessed increasing integration of thevirtues of these approaches. For example, multi-variate methods of the kind used in RIVPACShave been integrated with IBI developmentand there is increasing use of tools such as arti-ficial neural networks and self-organizing mapsin interpreting water-quality scores arrived byBIs and IBIs.

Major avenues of future R&D thrust includedeveloping the ability of the indices to accountfor nonmeasured parameters via correlation

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modelling. This will, on the one hand, reducethe costs of water-quality monitoring and, onthe other hand, will make it increasinglypossible to use the indices in conjunction withautomated water quality monitoring networks.

Just as some ‘global’ water-quality standardsare available in the form of standards set bythe World Health Organization, global WQIsfor some of the water use would be veryhelpful as they would enable the water qualityof a region being seen in a globally acceptablecontext.

There is a case for the development of multi-variate analysis methods with which ‘weights’can be assigned to different physico-chemicalparameters instead of doing it, as is common,with Delphi or with some kind of ad hocformula using water-quality standards. Theformer is very cumbersome and inevitablycarries an element of subjectivity while the latterapproach is totally ad hoc.

16.4. THE LAST WORD

There is one future trend about which it is notpossible to have any doubt: That is of rapidlyincreasing importance ofWQIs in people’s lives.With water demand running ahead of watersupply, and the quality of water that is availablesteadily declining, the importance of water ineveryone’s life across the world is set to increaseby the day. Water of good quality will be atincreasing premium and there will be evergreater need all over the world to segregatewater usable for drinking from the water usablefor other contact applications and from thewater usable only for irrigation, industry etc.These compulsions, in turn, would enhancethe necessity that water quality is quantified ina manner that it is intelligible to everyone. Forexample, a national water-quality index maysay that when any water has index score 80 orhigher, the water is fit for drinking and thatcloser the score is to the upper limit of 100, the

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16. WATER-QUALITY INDICES: LOOKING BACK, LOOKING AHEAD356

better the water is. It may also say, for instance,that a water with index score between 70 and80 may also be used for drinking providedthat it has been boiled for 5 minutes. Companiessupplying water will be providing its score forthe customer’s knowledge and choice. All thesehappenings are expected to make WQI a house-hold word in the near future.

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