Energy-water nexus of formal and informal water systems in Beirut, Lebanon

Abstract Many areas in the world with chronic and intermittent water shortages rely on informal water systems for much of their daily water needs with water from tanker trucks, purchased bottled water, rainwater cisterns, or pumped well water. These alternative sources all require varying amounts of energy. Water-energy nexus studies have not yet considered environmental impacts of informal water sources, specifically from an energy intensity and carbon emissions perspective. This study compares energy use and carbon emissions per cubic meter and per capita for both formal and informal water sources for a neighborhood in Beirut Lebanon. Energy use and carbon emissions are calculated for three delivery stages per source including pumping, treatment and distribution. The results show that informal sources have the highest energy use and carbon emissions. From the total water delivered to households, they account for 83% of energy use and 72% of carbon emissions per capita, even though they only provide 23% of total delivered volume per capita. Bottled water and distribution of water by tanker trucks have the highest energy intensity values per cubic meter of all water sources. Moreover, internal building water pumping, which is not typically accounted for, takes up to 14% of total energy use and 23% of total carbon emissions per capita compared to other water sources. To address model uncertainty, we conduct a sensitivity analysis, showing that the base model presented reasonably stable results and identifying the most sensitive parameters for further research. While informal sources help communities overcome water shortages they result with negative impacts. Strategies are proposed to improve the environmental performance of the Lebanese electrical grid, reduce water losses, replace inefficient truck engines and incentivize household to invest in low carbon technologies.