The water companies were asked to provide information about their current practices to calculate the ELL, which includes external costs and benefits (as shown in Table 4.1). However, it recognises that several approaches exist, and that regional differences should be taken into account (Tripartite Group, 2002). In 2008, Ofwat conducted further work to revise leakage based on a frontier approach to leakage target setting (WRc, 2008).