A Comparative Study of USA and Canadian Water Quality Index Models

Abstract

The US-based water quality index models originated from the National Sanitation Foundation (NSF) in additive (AWQI) and multiplicative (MWQI) forms in the early 1970s. The other model which has gained popularity in the recent years is Oregon Water Quality Index (OWQI) which is based on the harmonic averaging concept. The Canadian Council of Ministers of the Environment Water Quality Index (CCME WQI) (also referred to as Canadian Water Quality Index, CWQI in the text) was commissioned in 2001 to assess the water quality of surface waters across Canada. The United Nations Environmental Program (UNEP) has endorsed the CCME WQI (or CWQI) model suitable for grading the quality of drinking waters world wide. The index scores from all the models range from 0 to 100, higher scores alluding to better quality. The water quality is categorized in five grades [excellent, good, fair, marginal, poor], with differential system of ranking while using the index score values. The present study evaluated the water quality data from 30 river sites across the province of Ontario, Canada for 5-year period 2002–04 through 2006–08 (3-year running averages) for the comparison of aforementioned WQI models. The parameters currently used in calculating CCME WQI (or CWQI) score in Ontario are: ammonia, chloride, nitrate, phosphate, chromium, nickel, and zinc (seven parameters). The parameters hardness, pH and temperature are monitored but are used as modifying parameters, i.e., they are taken into consideration by modifying the guidelines or the objective functions of some of the former seven parameters. The study indicated that AWQI and MWQI scores tended to be much higher in comparison to the CWQI scores. As a result, the grades of the water quality for AWQI and MWQI turned out to be superior in relation to CWQI. In contrast, the correspondence in terms of water quality grades between OWQI and CWQI was much closer and better. Overall, the CWQI formulation appeared to be the most stringent, followed by OWQI model to grade the quality of water for the aquatic uses.