Development of a fabricated first-flush rainwater harvested technology to meet up the freshwater scarcity in a South Asian megacity, Dhaka, Bangladesh

The scarcity of freshwater in most of the megacities in the world is an important concern. In this regard, scientifically harvested rainwater could provide an effective measure to this crisis. In this attempt, we developed a cost-effective sensor-based automated first-flush rainwater harvesting system (RHS) to improve the freshwater scarcity and economic development of megacities like Dhaka, Bangladesh. To investigate the performance of the developed system, a suit of representative rainwater samples was systematically collected, preserved, and assessed between the months of July–December 2021 for water quality parameters such as physicochemical (pH, EC, TDS, DO, hardness, and alkalinity), anions (F−, Cl−, NO2−, NO3−, Br−, and SO42−), elemental (Ca, Mg, Cr, As, Cd, Hg, Pb, Be, Ni, Se, and Fe), and microbial contamination analysis. A Multiparameter digital meter and a titrimetric method were employed for measuring the physicochemical properties whereas elemental concentration was detected using an inductively coupled plasma-mass spectrometer and atomic absorption spectrometer. The changes in microbial contamination in the preserved rainwater were investigated from time to time during the whole experimental period. The findings showed that the mean pH (6.90) and concentrations (mg/L) of other concerning parameters such as TDS (15.5), DO (7.26), hardness (14.9), Cl− (3.59), NO3− (4.84), SO42− (4.62), Fe (<0.2), Cr (0.086 μg/L), As (0.224 μg/L), Cd (0.260 μg/L), Hg (0.270 μg/L), and Pb (5.530 μg/L) in the harvested rainwater samples were below the WHO drinking water guidelines and literature data implying that the harvested rainwater derived from the developed RHS is completely safe for drinking and other uses even in respect to the microbial contamination (total bacterial counts: 0–15 CFU/mL, and total and fecal coliform less than 1.8 MPN/100 mL) for long storage. Hence, this technology has a huge opportunity to mitigate safe freshwater scarcity and groundwater depletion issues, especially in megacities such as Dhaka, Bangladesh.