 of private capital as a way to shift the burden of funding from the public to the private sector. On the face of it, the water sector should be an attractive prospect: it is an essential service; it is technologically relatively low in risk and if reasonably well managed, offers steady though not spectacular returns. However, Ashley and Cashman note that private investment in the water sector is not without problems, as experiences in South America, South Africa and the Philippines suggest. Despite these difficulties, the involvement of the private sector in the public provision of services such as water is likely to grow in importance - especially given the huge engineering and financial challenges to be faced either in the provision of new infrastructure or the maintenance of existing assets. The nature of the relationship between the public and private sectors in this regard will have to evolve from the present models in order to gain greater political and social acceptance, especially in developing countries. Notwithstanding the possible growth in the role for the private sector, there is also potential for some forms of public financing, e.g. user fees, and the wider use of bonds. Demography Together with economic development, population growth is considered the most important driver of the demand for infrastructure. However, it is not the only demographic factor at play. For instance, Bohlin et al. acknowledge the importance of population ageing, of urbanisation in the developing world and of international migrations as important determinants of the expansion of telecom networks. Increase in the number of households could also be a factor here, as it is in the case of electricity. INFRASTRUCTURE TO 2030: TELECOM, LAND TRANSPORT, WATER AND ELECTRICITY - ISBN 92-64-02398-4 © OECD 2006 1. A CROSS-SECTORAL PERSPECTIVE ON THE DEVELOPMENT OF GLOBAL INFRASTRUCTURES TO 2030 The IEA chapter also notes that changes in the level and age composition of the population affect the level and composition of electricity dem