Managing urban water supplies in developing countries – Climate change and water scarcity scenarios

Abstract

Urban areas of developing countries are facing increasing water scarcity and it is possible that this problem may be further aggravated due to rapid changes in the hydro-environment at different scales, like those of climate and land-cover. Due to water scarcity and limitations to the development of new water resources, it is prudent to shift from the traditional ‘supply based management’ to a ‘demand management’ paradigm. Demand management focuses on measures that make better and more efficient use of limited supplies, often at a level significantly below standard service levels. This paper particularly focuses on the intermittent water supplies in the cities of developing countries. Intermittent water supplies need to be adopted due to water scarcity and if not planned properly, results in inequities in water deliveries to consumers and poor levels of service. It is therefore important to recognise these realities when designing and operating such networks.

The standard tools available for design of water supply systems often assume a continuous, unlimited supply and the supplied water amount is limited only be the demand, making them unsuitable for designing intermittent supplies that are governed by severely limited water availability. This paper presents details of new guidelines developed for the design and control of intermittent water distribution systems in developing countries. These include a modified network analysis simulation coupled with an optimal design tool. The guidelines are driven by a modified set of design objectives to be met at least cost. These objectives are equity in supply and people driven levels of service (PDLS) expressed in terms of four design parameters namely, duration of the supply; timings of the supply; pressure at the outlet (or flow-rate at outlet); and others such as the type of connection required and the locations of connections (in particular for standpipes). All the four parameters are calculated using methods and techniques that recognise the relationship between outflow at a water connection and the pressure experienced at that connection. The paper presents a case study where it is demonstrated that the new guidelines can provide an equitable and acceptable level of service throughout the design horizon of the project.

Introduction

Water demand already exceeds supply in many parts of the world, and more and more areas are expected to experience this imbalance in the near future. Water is required for agricultural, industrial, household, recreational and environmental uses. Demand for water for agricultural, household, recreational and environmental uses is rapidly increasing due to continuously increasing population especially in the developing world and due to growing awareness of environmental, health and recreational issues. In spite of the fact that national water policies of many countries place household and industrial water needs at a higher priority level over other uses, there are issues that limit the water availability for these uses at the points of consumption, resulting in water stress conditions. Many changes taking place at a rapid pace over different spatial scales including global climatic change, Landuse changes and environmental degradation, further aggravate this problem. At the same time, the cost of developing new sources or expanding existing ones is continuously increasing as the most accessible water resources have already been tapped (UNESCO, 2003).

The scarcity of water resources has brought into focus the urgent need for planned action to manage water resources effectively as it is widely acknowledged that water is a major limiting factor in the socio-economic development of a world with a rapidly expanding population. The United Nations in their Millennium Declaration draws attention to the importance of water and water related activities in supporting development and eradicating poverty (UN, 2003), specifically one of the targets of the goal 7 of the Millennium Development Goals (MDGs signed in 2000) is to halve the proportion of people without access to safe drinking water and basic sanitation. 2006 Millennium development report (United Nations, 2006) indicate that in spite of the significant achievement of reducing the fraction of people without access to safe water from 30% in 1990 to 20% in 2004, still there are wide disparities among countries.

Currently, some 30 countries are considered to be water stressed, of which 20 are absolutely water scarce. It is predicted that by 2020, the number of countries with water scarcity will likely to approach 35 (Rosegrant et al., 2002). More worrying is that it is the developing countries that face the greatest crisis and it has been estimated that by 2025, one-third of the population of the developing world will face severe water shortages (Seckler et al., 1998). Fig. 1 indicates the total non-irrigation water consumption (domestic, industrial, and livestock use) for the different regions of the world (Rosegrant et al., 2002). This figure highlights that it is in the developing world where there will be a drastic increase in consumption.

In general water supplies in cities are usually supply driven, meaning whenever there is a “shortage” the solution has to rely on the capital investment in new treatment and distribution networks. However, faced with the realities of rapidly growing populations and increasing urbanization and the increasing scarcity of capital for new water supply development projects, this approach alone is failing to keep up with the increasing demands. Hence, innovative demand management strategies need to be developed and the perception that water conservation measures are only as drought-relief mechanisms that result in reduced service levels has to be changed (UN-HABITAT, 1999).

This paper discusses the various issues that limit the water availability for non-irrigation uses and presents a model developed for one such conservation measure, i.e. intermittent water distribution systems for managing limited water resources sustainably and equitably in the urban communities.