Cities are increasingly depending on energy‐intensive water sources, such as distant rivers and the ocean, to meet their water demand. However, such expensive sources could be avoided using alternative local sources of water such as wastewater, rainwater, and stormwater. Many cities do not have robust accounts of those localized water resources, as estimating those resources requires comprehensive accounting in complex urban water systems. In this article, we investigate whether an urban metabolism evaluation framework built on the urban water mass balance can help analyze these resources, especially in a rapidly growing developing city. We first refined the water mass balance equation developed by Kenway and his colleagues in 2011 for a developing country context with the inclusion of some significant components such as system loss. Then, we applied the refined equation for the first time to Bangalore city in India, a developing country, for the year 2013–2014 as a real case example, which is a rare water mass balance analysis of its kind. The refined equation helped analyze Bangalore's urban water system. The total available wastewater, stormwater, and rainwater were 656 gigaliters (GL). The gap between water demand and supply could be met if 54% of this recycled potential were harnessed. Wastewater had enough potential (362 GL) to replace the whole centralized water supply from the Cauvery. A scenario analysis showed that the gap between water demand and supply in 2021 can be met if 60% of total recycled potential is utilized. This approach can be used to help other cities identify the potential of alternative water sources and support integrated water planning and monitoring water metabolic performance.