Wellington Water Ltd manages a dynamic water supply system that relies on water drawn from two surface water collection schemes and an aquifer. This presents unique challenges when assessing the long term ability of the system to withstand drought or the operational risk of supply shortfall during summer. Wellington Water uses a strategic planning tool called the Sustainable Yield Model (SYM) to support its decision making. The SYM simulates the entire water supply system including resource consents and infrastructure constraints. The SYM has recently been comprehensively upgraded through a project completed by the National Institute of Water and Atmospheric Research (NIWA). The project is future-proofing the SYM by streamlining the assessment process and incorporating the latest water demand and climate change information. Wellington Water uses the SYM to assess the future upgrades needed to maintain the Wellington Region’s drought level of service in the context of increasing demand, changing climate and rising sea level. The SYM is also used in an operational capacity during summer to support a risk based assessment of the likelihood of supply shortfall and the need for watering restrictions. This paper outlines how the SYM is used for strategic and operational planning at Wellington Water.