  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.
