Yield, water use and water-use efficiency (WUE) in the high-rainfall zone of Tasmania are highly variable because of environmental and agronomic constraints to grain production that limit yield potential. The expansion of irrigation infrastructure in Tasmanian production systems with access to low-cost, plentiful irrigation sources will also influence these components in some areas. This paper reports on desktop modelling studies that aimed to benchmark wheat WUE and to explore the sensitivity of yield, water use and WUE to changes in management practice in a high-rainfall environment. Here, WUE was defined as: grain yield/(evapotranspiration   drainage   runoff). The crop simulation model APSIM-Wheat was used to quantify key water balance elements and estimate ‘attainable’ and ‘potential’ WUE and grain yield for 27 wheat trials. The upper limit for WUE was ∼30 kg/ha.mm in excess of 180 mm evaporation, which is 16% higher than previous estimates at this southerly latitude for wheat. Attainable WUE ranged from 58% to 100% of potential WUE and was limited by nitrogen supply and water loss through evaporation, drainage and runoff. Model scenarios showed that co-limitation of inputs of nitrogen and irrigation was an important driver of grain yield and WUE. The implications of this research on crop management and production in temperate, high-rainfall environments are discussed.