Analysis of first flush to improve the water quality in rainwater tanks

Abstract

Although most Australians receive their domestic supply from reticulated mains or town water, there are vast areas with very low population densities and few reticulated supplies. In many of these areas rainwater collected in tanks is the primary source of drinking water. Heavy metals have recently become a concern as their concentration in rain water tanks was found to exceed recommended levels suitable for human consumption. Rainwater storage tanks also accumulate contaminants and sediments that settle to the bottom. Although not widely acknowledged, small amounts of contaminants such as lead found in rain water (used as drinking water) may have a cumulative and poisonous effect on human health over a life time. This is true for certain factors that underlie many of the chronic illnesses that are becoming increasingly common in contemporary society. The paper reports on a study which is part of a project that aims to develop a cost effective in-line filtration system to improve water quality in rainwater tanks. To enable this, the characteristics of rainwater need to be known. One component of this characterization is to observe the effects of the first flush on a rainwater tank. Samples of the roof runoff collected from an urban residential roof located in the Sydney Metropolitan Area in the initial first few millimetres of rain were analysed. The results show that bypassing the first 2 mm of rainfall gives water with most water quality parameters compliant with the Australian Drinking Water Guidelines (ADWG) standards. The parameters that did not comply were lead and turbidity, which required bypassing approximately the first 5 mm of rainfall to meet ADWG standards. Molecular weight distribution (MWD) analysis showed that the concentration of rainwater organic matter (RWOM) decreased with increasing amount of roof runoff.

A review on physicochemical and microbiological contamination of roof-harvested rainwater in urban areas

“…Martinson and Thomas (2005) recommend values varying from 1.0 to 8.5 mm according to the mean runoff turbidity on wet days following at least 3 dry days, and the intended turbidity level for the rainwater in the tank. Kus et al (2010) obtained that bypassing the first 2 mm of rainfall gives a rainwater quality compliant with most of the parameters of the Australian Drinking Water Guidelines (ADWG) standards, with the exception of lead and turbidity, which required 5 mm of first-flush to meet these standards. In summary, by using a well-regulated fistflush deviation device, the quality of the harvested rainwater can be improved dramatically.…”

Evaluation of rainwater harvesting in Portugal: Application to single-family residences

“…Comparing with the results of Mendez et al (2011), it is clear that the rainwater quality depends on the location. Kus et al (2010a) found that diverting the first 2 mm of rainfall assures compliance with the Australian Drinking Water Guidelines (ADWG) standards except for lead and turbidity, which required bypassing approximately the first 5 mm of rainfall. A first flush system improves the physicochemical quality of collected rainwater but it cannot avoid microbial contamination of stored rainwater (Gikas and Tsihrintzis, 2012).…”

Impact of Climate Change on Reliability and Water Saving Potential of Domestic RWH Systems in Dhaka.

“…For frequency analysis of dry duration, rainfall events below 2 mm were set as dry days. Previous studies conducted by (Guo and Baetz, 2007) and (Kus et al, 2010) have shown that 2 mm of first flush can significantly improve quality of rainwater collected. (Martinson and Thomas, 2005) showed that each 1 mm of rainfall diverted in first flush can roughly reduce 50% of remaining turbidity load from collected rainwater.…”