A conceptual wetland model was developed to describe the interactions between a wetland, the surrounding catchment, and the local groundwater. Numerical evaluation of the wetland water balance was achieved by applying a bucket model. The model required little calibration and used physically based catchment properties and recorded climatic data sets. Model flexibility lends itself to application across a broad range of wetland types from seasonally to permanently inundated (or saturated) systems. The model was applied to Loch McNess, a permanent open water body of maximum depth 3.4 m located on the Swan Coastal Plain in Perth, Western Australia. Groundwater flow was found to dominate the wetland water balance. The local groundwater was shown to be interactive, responding to specific conditions within the wetland. The model enabled differentiation between groundwater components. Flow paths were separated into groundwater inflows and outflows, and an overflow mechanism connecting the wetland to the nearby cave system was identified. Results from this study show that the bucket model can be used to isolate dominant hydrological processes of a wetland system, focus field studies of wetland hydrology, or facilitate management of the system.