Abstract
In south-west coastal Bangladesh, water salinity has been greatly recognized as one of the significant
problems in the life of coastal people. Recently the south-west coastal people are facing extreme difficulties
in accessing safe drinking water and they have practiced various water consumption systems according to varying levels of water availability such as rainwater, PSF water, protected pond water, MAR water, tube
well water and refined supply water, etc. For mitigating the growing water crisis in coastal regions, the present study was conducted to provide information on variability of rainfall, quality and suitability of existing drinking water collected from different sources such as groundwater, PSF water, MAR water, protected pondwater, harvested rainwater with harvesting systems and water treated with slow sand and
biosand filters with their performances for drinking water. Rainfall data were analysed to detect the annual rainfall trends of south-west coastal regions of Bangladesh. Water samples from different existing water
sources were collected through purposive sampling during January 2015 to December 2017. To analyze the hydrochemical data of waters collected from different sources, principal component analysis, Pearson
correlation matrix, Bivariate plots, Piper trilinear diagram, Gibbs diagram and Chadha's plot were
conducted. To assess water quality and geochemical properties, water quality index (WQI), total hardness (TH), electrical conductivity (EC) and total dissolved solids (TDS) were measured. Microbiological quality
and health risk assessment were performed for PSF water and harvested rainwater samples. In this study, the spatial and temporal variability of precipitation has been investigated in south-west parts of Bangladesh over
the period of 1948-2016 on annual, seasonal and monthly basis. Positive trends were found in south-west
stations of Khulna and Satkhira. In case of ground water, aquifer was intermediate between rock and
evaporation-dominance, affected by sea water and Na"-CI type indicating a seawater influence. On the basis
of EC and TH more than 90% samples fell in unsafe category with minor falling in safe zone for drinking.
PSF-source water and PSF-treated water were almost similar in respect of EC, TDS and major ions including
Na and Cl. They were also evaporation-dominance and Na*-Cl type. As per EC, more than 50% samples
were high saline. On the basis of TH, more than 60% samples were hard and very hard water categories.
Health risk was assessed and both source and treated waters were found in intermediate and high risk categories. In rainfed protected pond, water samples were evaporation-dominance and Na-CI- type
influenced by sea water. According to EC and TH classification, more than 70% samples grouped in unacceptable category for drinking. MAR water showed that all the samples were also evaporationdominance and Na+-CI- type but much better than ground water in respect of TDS, Na and CI-. As per
WQI, 60% samples were found in poor water category. Although, rainwater was found excellent in terms of WQI, EC, TDS and major ions, but indicator organisms were detected in all samples of harvested rainwater. High microbial contamination was found at low, intermediate and high risk categories in wet season
compared to dry season. For rainwater harvesting, among the roofing materials used in south-west coastal
belts, the highest (60%) used material was CI sheet (Tin). Among different storage tanks, plastic tank was
found the highest used (53%) tank for storage harvested rainwater. Among the existing rainwater harvesting and storage systems, rainwater collection and storage in plastic tank was found to be the best. In comparison with the performance of slow sand filter, biosand filter was found the most effective to reduce 99% to
99.56% pathogens from harvested rainwater. From this study, it is evident that water collected from all possible sources in coastal areas such as groundwater, PSF water, MAR water and protected pond water
were not found suitable due to high salinity, higher presence of TDS, higher cations and anions. High pathogenic contaminations were found in harvested rainwater. As a result, these waters were not fully safe
for human consumption. Harvested rainwater collected from plastic storage tank treating by biosand filter
may be a suitable technology for sustainable and quality drinking water supply in south-west coastal Bangladesh.