Abstract
Water security is one of the pressing challenges in sustainable cities of the future as the demand for freshwater increases along with the environmental stresses caused by climate change. For example, Metro Manila, Philippines, experienced a water crisis brought by increasing demand and lasting impacts of climate change in 2019. In response, the Metropolitan Waterworks and Sewerage System (MWSS), together with its water concessionaires, Maynilad Water Services, Inc. (Maynilad), and Manila Water Company, Inc. (Manila Water), laid out a water infrastructure plan to bridge the water deficit. However, the decision-making process can be iterative and participatory characterized by uncertainty. This study thus proposed decision-making framework to explore the possibility of alternative sustainable water supply networks in Metro Manila through P-graph and analytic hierarchy process (AHP). Alternatives considered were saltwater desalination, rainwater harvesting, and non-revenue water (NRW) recovery. A sustainable network was defined as having low operational (OPEX) and capital expenses (CAPEX), high water security, and low global warming potential (GWP). Relative weights of sustainability, derived through AHP, showed that water security was the most important sustainability criterion among the surveyed experts in water supply construction and operations. P-graph simulations yielded optimal and near-optimal solutions indicating the possibility of not including the controversial water supply infrastructure project (Kaliwa dam) as a prioritized management option. Instead, sustainable supply networks relied on desalination, rainwater harvesting, and NRW recovery are identified as the main components of the optimal water supply network. Overall, the study suggests that better planning and accounting for sustainability is needed to identify and implement projects that do not only serve the short-term needs but also integrate well into the long-term plans.
