A large proportion of the overdispersion observed in the zonal lead compliance distribution (see Figure ) is accounted for by the zonal variation in the proportion of properties with lead service pipes, and this information is required to interpret zonal compliance in different zones. After accounting for the heterogeneous nature of the zonal LPDs, "Supply" was found to be a statistically significant parameter. However, the scope for re-optimising treatment was limited to a few small supplies. Further improvements in compliance will make it even harder to identify suitable supplies for re-optimising treatment using compliance data.