enerally higher living standards and greater political articulation, every increase in water quantity will correspondingly give rise to calls for better quality, and since rising urban demands mean more residential sewage and industrial pollution, every increase in consumption could lead to concurrent deterioration in water quality. Thus the problems can become associated with allocation and management rather than resource development. The efficiency with which water is used has become a major consideration, especially in urban supply as the scale of losses has become increasingly apparent. A significant percentage of distributed water never reaches the final user but is lost due to leakage. Average leakage rates for Public Water Supply (PWS) range from 10% in Austria, Australia and Denmark to 33% in the Czech Republic (OECD, 1999). In the United Kingdom in the 1980s some 30% of all water was lost from water distribution systems, and in some parts of London that figure reached 60% (The Guardian, 2003). Such problems are most acute in long established urban areas with ageing assets. Water infrastructure such as pipes INFRASTRUCTURE TO 2030: TELECOM, LAND TRANSPORT, WATER AND ELECTRICITY - ISBN 92-64-02398-4 © OECD 2006 5. THE IMPACTS OF CHANGE ON THE LONG-TERM FUTURE DEMAND FOR WATER SECTOR INFRASTRUCTURE can be expected to last for between 50 and 100 years depending on conditions, implying replacement rates of 2% per annum. Most systems in urban areas were laid at the beginning of the 20th century but replacement work has often been neglected: 0.01% in London and 0.8% in Munich for example (SAM, 2004). A major difficulty is in defining what levels of leakage may be acceptable from "public" mains. In England and Wales, Economic Level of Leakage (ELL) is used to specify targets for the water companies. ELL represents an agreed leakage rate above which it is believed economic to tackle the problem and below which it would supposedly cost more than it would save to deal with. ELL suffers from the notorious difficulty