Volume reduction of water samples to increase sensitivity for radioassay of lead contamination

The World Health Organisation (WHO) presents an upper limit for lead in drinking water of 10 parts per billion ppb. Typically, to reach this level of sensitivity, expensive metrology is required. To increase the sensitivity of low cost devices, this paper explores the prospects of using a volume reduction technique of a boiled water sample doped with Lead-210 ($^{210}Pb$), as a means to increase the solute's concentration. $^{210}$Pb is a radioactive lead isotope and its concentration in a water sample can be measured with e.g. High Purity Germanium (HPGe) detectors at the Boulby Underground Germanium Suite. Concentrations close to the WHO limit have not been examined. This paper presents a measurement of the volume reduction technique retaining $99\pm(9)\%$ of $^{210}$Pb starting from a concentration of $1.9\times10^{-6}$ ppb before reduction and resulting in $2.63\times10^{-4}$ ppb after reduction. This work also applies the volume reduction technique to London tap water and reports the radioassay results from gamma counting in HPGe detectors. Among other radio-isotopes, $^{40}$K, $^{210}$Pb, $^{131}$I and $^{177}$Lu were identified at measured concentrations of $2.83\times10^{3}$ ppb, $2.55\times10^{-7}$ ppb, $5.06\times10^{-10}$ ppb and $5.84\times10^{-10}$ ppb in the London tap water sample. This technique retained $90\pm50\%$ of $^{40}$K. Stable lead was inferred from the same water sample at a measured concentration of 0.012 ppb, prior to reduction.