The confidence limits for the calculated non-compliance for a supply can be determined by using the exact binomial method. Many of these confidence ranges include the regional average non-compliance value (see Figure ) but some are above and some below the regional level of non-compliance. At the 95 % level of confidence 3 supplies can be regarded as significantly greater than the predicted value and 2 significantly lower. This is much higher than expected by chance. Thus, it might be appropriate for those supplies which are statistically greater may require additional treatment or lead pipe replacement. Equally treatment conditions can be reasonably lowered for those supplies which significantly less than predicted. The approach taken for all zones can be applied to all zones in a single supply. However, this approach is limited to large supplies where number of samples is sufficient.