In particular, surface water interactions with groundwater, and the diffusion of pollutants at the regional level, are not always perfectly known. They do not explicitly cover risks to ecosystem resilience, subsuming them instead in the others. For example, flood control and water storage may rely on flood plains, wetlands or groundwater recharge, and water quality and wastewater treatment affect freshwater system resilience. A fourth subsection will discuss partnerships as a mechanism for implementing rural-urban co-operation.