Longitudinal assessment of rainwater quality under tropical climatic conditions in enabling effective rainwater harvesting and reuse schemes

A longitudinal harvested rainwater quality monitoring study was undertaken at 6 sites within Selangor, Malaysia over a period of 8 months. Overall, harvested rainwater is of good quality, falling within the Malaysian recreational water quality Class IIB standards with exceptions for pH (18/92), ammonia (1/92), phosphates (3/92), and total coliforms (8/92). A large number of samples tested positive for Escherichia coli (22/92), total coliforms (64/92) and Chromobacterium violaceum (7/92), showing that disinfection of harvested rainwater is mandatory prior to reuse. 2/37 harvested rainwater samples exceeded lead limits in Malaysian drinking water standards, showing that consuming rainwater without additional treatment may pose a health risk. Mixing harvested rainwater with groundwater resulted in higher phosphates and total coliforms. Rainwater collected during the wet seasons have higher concentrations of suspended solids, turbidity, and Escherichia coli than dry seasons due to the antecedent dry period. Last but not least, both principal component analysis and positive matrix factorisation were conducted on 37 samples to apportion pollutant sources in harvested rainwater. 7 principal components were identified, namely: industrial dust, steel, roadside dust, faeces, organic decay, fertilisers, and plumbing. The results from principal component analysis and positive matrix factorisation were in agreement, although the latter identified mains water top-up as an additional factor responsible for dissolved solids. Both techniques are effective at apportioning pollutant sources in harvested rainwater, and show that a rainwater harvesting system should be designed carefully to reduce contributions from steel, plumbing, organic decay, bird faeces, industrial dust and roadside dust.