Whilst acknowledging that current leakage rates are below the national average, loss of 110 litres per household compared to average usage of 140 litres daily, seems excessive.  
Within the context of leakage vs usage, a target for leak reduction of 15% seems rather unambitious in my view.  I appreciate that leak detection is difficult and costly but nevertheless would have thought it cost effective to divert significant resources to reducing the losses by a minimum of 50% over 5 years if not more.
My personal view is that leakage should never exceed 2 - 5%.