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

摘要

Although most Australians receive their domestic supply from reticulated mains or town water,nthere are vast areas with very low population densities and few reticulated supplies. In many ofnthese areas rainwater collected in tanks is the primary source of drinking water. Heavy metalsnhave recently become a concern as their concentration in rain water tanks was found to exceednrecommended levels suitable for human consumption. Rainwater storage tanks also accumulatencontaminants and sediments that settle to the bottom. Although not widely acknowledged, smallnamounts of contaminants such as lead found in rain water (used as drinking water) may have ancumulative and poisonous effect on human health over a life time. This is true for certain factorsnthat underlie many of the chronic illnesses that are becoming increasingly common inncontemporary society. The paper reports on a study which is part of a project that aims tondevelop a cost effective in-line filtration system to improve water quality in rainwater tanks.nTo enable this, the characteristics of rainwater need to be known. One component of thisncharacterization is to observe the effects of the first flush on a rainwater tank. Samples of thenroof runoff collected from an urban residential roof located in the Sydney Metropolitan Area innthe initial first few millimetres of rain were analysed. The results show that bypassing the firstn2mm of rainfall gives water with most water quality parameters compliant with the AustraliannDrinking Water Guidelines (ADWG) standards. The parameters that did not comply were lead andnturbidity, which required bypassing approximately the first 5mm of rainfall to meet ADWGnstandards. Molecular weight distribution (MWD) analysis showed that the concentration ofnrainwater organic matter (RWOM) decreased with increasing amount of roof runoff.