In the UK the performance of utility operators is monitored by a regulator who publishes annual reports on their compliance. In addition, water utilities provide on-line compliance data to customers for each water supply zone. It is therefore not surprising that operators pay particular attention to compliance as a measure of risk. In any water supply zone with a population greater than 5000 the number of regulatory audit samples in any year is 8. This frequency is considered too small to assess zonal risk particularly since it is not known which properties have lead service pipes, which creates a large additional random factor in the RDT data. For this reason, most companies will have a much larger operational sampling programme to help identify risk.