This paper examines the future water supply situation in Adelaide, a relatively dry city in South Australia, in the driest populated continent on earth. Using the Systems Approach, we analyse a diversified strategy with a new portfolio mix of core bulk water: (i) rainfall independent desalinated water from the ocean and (ii) rainfall dependent water from catchments including the Mount Lofty Ranges (MLR) and water piped from the Murray‐Darling Basin (MDB) including via the Mannum‐Adelaide Pipeline. Our focus is on the quantity, indicative costs and risks of water supply, and associated augmentation choices and trade‐offs, over the next century to 2114. We model using historically‐based projections of drought risks and growth pressures, reflecting a century of rainfall and catchment inflow data based on historical data obtained from Australian Bureau of Meteorology and SA Water, water services in South Australia. A major finding through our simulations is that demand more than drought is the real and looming source of long term shortages of supply relative to demand. However, short‐term risks differ depending on the composition of the supply portfolio. Expanding dams and pipelines will allow a greater share of MDB water to be accessed, but at substantial drought and political risk. Over the next 100 years demand may nearly treble, but the water volumes and the battles over sharing MDB water, dams and pipelines may remain the same. Thus, it is the gap between demand and supply that, absent desalination plants, will generate increasing water supply crises in Adelaide and elsewhere.