We recently reported on water quality in rain tanks.
Magyar, M. I., Ladson, A. R., Diaper, C., Mitchell, V. G. (2014) Influence of roofing materials and lead flashing on rainwater tank contamination by metals. Australian Journal of Water Resources 18(1): 71-84.(paper at journal) (abstract at informit)
Abstract: The quality of rainwater collected in polyvinyl chloride (PVC) tanks from six trial roofs (glazed tile, pre-painted steel and aluminium-zinc coated steel, each with and without uncoated lead flashing) was monitored for nine months. Samples of water and sediment were collected at three monthly intervals and analysed for concentrations of metals (Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn), in order to determine the influence of roof materials and uncoated lead (Pb) flashing upon metal contaminations within the tanks. Lead concentration in tank water exceeded Australian Drinking Water Guidelines for all roof types where there was lead flashing. Lead flashing also contributed to contamination of tank sediments. In all cases, pH was low which contributed to a large proportion of lead being in the dissolved form.
Unfortunately, our response is yet to make it into the journal but is available by this link.
We also extend these arguments in a book chapter:
Magyar, M. I. and Ladson, A. R. (2015) Chemical quality of rainwater in rain tanks. In: Sharma, A., Begbie, D. and Gardner, T. Rainwater tank systems for urban water supply: design, yield, energy, health risks, economics and social perceptions. IWA publishing. pp 207-224. Link to Chapter 9.