Development of a methodology for sustainable conversion from an intermittent to a continuous water supply system

Abstract

Intermittent water supply systems (IWSS) supply water to about one-third of consumers in Africa, half in Asia and two-thirds in Latin America. Despite their wide application, IWSS present many problems that can be overcome by conversion to continuous water supply (CWS). However, conversion to CWS is difficult due to many interconnected IWSS causal factors. In this research, a methodology aimed at ensuring sustainable conversion from intermittent to CWS through increased understanding of the different causal factors is proposed. Among the eight identified causal factors are poor governance, demographic and economic dynamics. To incorporate uncertainties linked to the evolution of the causal factors, the methodology uses scenarios. Four scenarios (business as usual, consumption demand management, non-revenue water (NRW) management, and holistic) are developed for water supply systems using the drivers of water demand and the two axes scenario development method. For hydraulic analysis, a method for modelling IWSS is developed. Application of the “Global Scenario Group” scenarios to the Lusaka water supply network (LWSN) shows that Zambia is currently under the Market Forces scenario which has implications of poor revenue generation from water sales. Application of the developed scenarios shows that the NRW management scenario, which corresponds to the water supply investment master plan for Lusaka city, is not sustainable because the targeted reduction of NRW to 15% of the input volume by the year 2035 is not attainable. Moreover, if all the residents are considered, there will be a water deficit of 17,831 m3/d even if the 15% NRW reduction target was met. The most sustainable scenario, which will result in a water surplus of 10,287 m3/d, is the holistic scenario. However, its attainment requires concerted efforts to change the course of development from the unsustainable scenarios. The LWSN’s Chelstone zone’s 2035 topology is proposed following the optimisation of the zone’s scenario-based rehabilitation problems.