As flood risks intensify due to climate change and urbanization, integrating effective environmental solutions into urban settings has become critical. Blue-green infrastructure—combining water management, vegetation, and recreational spaces—offers significant potential for mitigating flood risks, reducing urban heat island effects, and enhancing quality of life. A key strategy involves transforming urban stormwater from a nuisance into a resource supporting constructed wetlands, which foster biodiversity, ecological resilience, and accessible green spaces within dense urban centres. Gazelle Valley Urban Nature Park in Jerusalem exemplifies this integration within Israel's densely populated capital. Established through collaboration among local residents, activists, social organizations, and the Society for the Protection of Nature in Israel, the park represents a major social and environmental achievement. Designed to high ecological standards, it has become a popular destination for residents and visitors, providing a model for embedding eco-hydrological solutions in urban landscapes. The park's water system relies on stormwater during the wet season (winter) and treated wastewater during the dry season (summer). We monitored and analyzed these alternating water sources through detailed laboratory investigations to characterize their composition and properties. Results reveal that alternating salinity and organic matter concentrations directly affect pH, dissolved oxygen, redox potential, that may affect the concentration and bioavailability of various metals. These findings highlight the geochemical risks associated with integrating urban surface water into constructed wetlands and underscore the importance of careful water quality management in nature-based solutions.