WATER QUALITY INDEX (WQI) CALCULATION FOR THE EVALUATION OF PHYSICO-CHEMICAL QUALITY OF RAINWATER COLLECTED IN RESERVOIRS FULL OF SAND (RFS)

WATER CHEMISTRY

The RFS system is an innovation of rainwater storing in Madagascar, it can be considered as an alternative system for supplying water to the population, especially in Southern Madagascar. The Androy and Anosy regions, repeatedly encounter periods of severe drought, the precipitation as well as infiltration are low while evapotranspiration is high. Not only the water supply for the population of these areas still remains a major challenge but the concern of water quality is another problem too, is why we have highlighted from this study examines the physico-chemical quality of this recovered rainwater from the calculation of its water quality indices (WQI) according to their storage.Indeed the WQI is a numerical expression used to assess the overall water quality from a large amount of data and it is easily understood by managers and decision makers. In this study, the WQI has nine physicochemical parameters namely: pH, conductivity, turbidity, calcium Ca2 +, sulfate SO4-, nitrate NO3-, Chloride Cl-, and magnesium Mg2 + which are used to estimate the overall quality of the rainwater collected in the RFS system compared to the rainwater collected in different storage facilities. Fourteen (14) water samples are taken, including three samples from four sites where stagnant water is found in southern Madagascar, three water samples traditionally treated with rohondroho (Alluaudia dumosa) and kibahy (Terminalia monoceros) plants, a treatment method used by the population in southern Madagascar to treat water for human consumption, four samples of rainwater stored in different types of reservoirs and three samples taken from the RFS in Masindray and Ambohidratrimo. The WQI during this study has showed a differentiation in the quality of the water according to the types of storage of the collected rainwater. For stagnant rainwater, the level of deterioration of water quality is significant depending on its lifespan. The treatment of water by plants only improves its physical quality, more precisely its turbidity, but increases the quantity of ions dissolved in the water. Furthermore, the quality of the water recovered in a RFS system show a good quality as far as physicochemical matter is concerned.

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