006 5. THE IMPACTS OF CHANGE ON THE LONG-TERM FUTURE DEMAND FOR WATER SECTOR INFRASTRUCTURE 2. Water resources - abstraction (and possibly storage) for human needs. The source can be upland rivers, lakes, lowland surface water, groundwater, sea or brackish sources or from evaporation systems. 3. Water supply network, including inputs from abstraction, treatment, storage and distribution, and outputs, including management of residual sludge. 4. Wastewater system, including stormwater and sanitary drainage, treatment, effluent disposal and management of residual sludge. Of these, in urban areas in the developed countries, the networks in 3) and 4) are generally the most valuable assets, comprising some 60-80% of the total value of all urban water and wastewater systems. For example, in the United Kingdom, the current value of existing sewage assets alone is some USD 200 billion. Service standards or levels are important in terms of assessing the current state of and demand for water-related infrastructure. These vary worldwide and are also not static, with ever increasing standards expected in the developed world and a bare minimum standard in a number of other countries. In the developing world, large networks and end-of-pipe treatment plants are being installed, even though "ecosanitation" is likely to be a more appropriate form of infrastructure, particularly in the less dense settlements. This is low-technology using VIP latrines and local water supplies stored and treated with basic but adequate standards. Joining the supply side to the waste side with reuse and recovery, a feature of ecosanitation, also makes nutrient and energy management more efficient. Even in developed countries, "eco-villages" in Sweden aim for a zero emission, supply-based water system. This approach is echoed in the WSSTP (2005) strategic research agenda, and in the 4th World Water Forum (in Mexico, March 2006) where Integrated water Resource Management (IWRM) is seen as a major solution option for the future (Sommen, 2006). Notwithsta