A very basic model that employs default settings can be obtained by modeling an aquifer system where recharge (input of water) is balanced exactly by surface seepage to gaining water bodies (loss of water). More complexity can be realized through the addition of other sources or sinks (for example, extraction and injection wells, losing streams or rivers, etc.) These features can be added to the model incrementally. In general it is best to start with a very simple model and add complexity confirming at each step that the model is still behaving as you would anticipate under the defined conditions.