In this report, I describe a model which simulates the development over many decades of the population growth, GDP growth, food demand, crop production (and trade), and water use in Pakistan. The model comprises several sub-models dealing with the individual aspects of population growth, GDP growth, food demand, agricultural production (including main imports and exports), water availability, water use in irrigation, hydropower production and energy use in groundwater pumping. While each sub-model is simple, combined they are complex. The use of the model is described via a demonstration which simulates the development of Pakistan from 1960 to 2050. The input data and parameters are described in detail. The demonstration is not calibrated to fit the observed data optimally; in a complex model of this type, there is unlikely to be a unique best-fit set of parameters. Rather, it is a plausible set of parameters. The demonstration simulates reasonably well a large number of different macro-level effects from population growth to GDP growth, from food demand to food production, from river flow to water use. The model is suited to exploring the relative importance of a wide range of biophysical and policy impacts, including population and poverty policy, economic growth impacts, food and agricultural policies, water allocation (including to the environment, as indicated by flows to the delta), climate change, and dam sedimentation. It is also well suited to the exploration of uncertainty in all of those aspects.