A key assumption of the Uniform Poisson Model is that the proportion of properties that are lead (this will be referred to as lead pipe density with the acronym LPD) is the same in all zones. However, experience indicates that there is considerable variation in LPD across zones. Variation in LPD across zones could account for the observed overdispersion. Unfortunately, like most utilities there are no substantive historical records of the materials used for service pipes. Fortunately, an opportunity arose during a programme of free water meters installation to gather information on the internal pipe materials at 69,506 properties. This data was geocoded using property post codes as per water quality data. This allowed each result to be assigned a property age-band and a zone. As can be seen from Figure lead pipe density varied widely across zones and ranged from 0 to 60 %. A chi-squared test confirmed that the zonal lead pipe density was non-random (𝜒 2 of 3779 compared to a test statistic of 313). A plot of lead pipe density against property age band (Figure ) is remarkably like that found for lead compliance (Figure ). Plotting lead compliance versus LPD for each property age band shows a significant correlation (Figure ). It supports the view that a large part of the non-random variation in lead non-compliance is due to the variation in lead pipe density, and hence the need for it to be included in any explanation for the variation of lead compliance between zones. It would be expected that non-compliance should be a linear function of lead pipe density. Carrying out a linear regression, taking into account the error in both variables, gives the relationship between lead non-compliance, NC, and the lead pipe density as 𝑁𝐶 = 0.18 + 4.80 * 𝐿𝑃𝐷