 Africa, as those countries here represent the majority of the less developed countries, which are particularly important with respect to the Millennium Development Goals. 2. Past trends in infrastructure investment Introduction Access to water and sanitation infrastructure is reportedly now more equitable than for most other main infrastructure provision (Fay and Yepes, 2003), with an accessibility ratio of high to low income of 1.3 for water and 2.2 for sanitation. Interactions between services are also important, as transport systems are needed to build and service infrastructure and waste systems can confound effective drainage. Energy is required increasingly worldwide, and there are existing and proposed conjunctive use schemes with large water resources and energy generation from hydropower. In developed countries much more pumping of wastewater and high-energy treatment has become common; in Europe this is due to the Urban Wastewater Treatment Directive, and in the United States to high-energy disinfection of sewage effluents. In developing countries the interaction between agricultural demand for water and human direct use is important in rural areas, as is the use of human waste as fertiliser, whereas in urban areas the main problem relates to the lack of solid waste handling systems. The latter situation leads to refuse collecting in wastewater channels, causing blockage, flooding and human health impacts. Investment in infrastructure has varied greatly globally. In general, water services require high rates of capital and maintenance investment with a low return on assets (typically 5%). Nevertheless, returns are low risk - as illustrated by the English water companies, where there is a high level of indebtedness but good returns for investors. While the populations of much of Western Europe, North America and most of the OECD countries now have effectively full access INFRASTRUCTURE TO 2030: TELECOM, LAND TRANSPORT, WATER AND ELECTRICITY - ISBN 92-64-02398-4 - © OECD 2006 5. THE IMPACTS OF CHANGE ON 