The concept of indexing water with a numerical value to express its quality, based on physical, chemical and biological measurements, was developed in 1965 by US based National Sanitation Foundation (NSF). In NSFWQI, the selection of parameters is based on Delphi method and these models were formulated in additive and multiplicative forms. The models were implemented across various states in the US while being continually refined. One refined form is known as Oregon Water Quality Index (OWQI). The index enjoys the advantage of being free from the arbitration in weighting the parameters and employs the concept of harmonic averaging. Another model of WQI from Europe (Spain) is that of Bascaron (Bol. Inf. Medio Ambient. 9:30–51, 1979), which is based on the normalization of the concentrations of the water quality parameters and then aggregating them through an additive model with suitable weights attached to the parameters involved. The major differences in various WQIs are based on the mannerism of statistical integration and interpretation of parameter values. A totally different approach was adopted in the Canadian Water Quality Index also known as Canadian Council of Ministers of the Environment Water Quality Index (CCME WQI). CCME WQI and is also being used by many countries all over the world and has also been endorsed by United Nations Environmental Program (UNEP) in 2007 as a model for Global Drinking Water Quality Index (GDWQI). The most commonly used parameters are dissolved oxygen, pH, turbidity, total dissolved solids, nitrates, phosphates, metals among others. All indices have one or other limitation and the search for a perfect one is still a challenge.
Canada Centre for Inland Waters, Ecological Monitoring and Assessment Network Coordinating Office, Wildlife and Landscape Science Directorate, Science and Technology Branch, Environment Canada, Burlington, Canada
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