With over 84% of Australians living in urban areas (populations over 30,000), the outcome of the current debate on water use in cities and how to match water demand to supply under both current and future climates, has the potential to affect many Australians. Lacking in this debate is a sound quantitative basis for assessing the environmental and economic benefits of water use in urban areas.As an example, while water sensitive urban design (WSUD) is widely accepted as a tool to manage the impacts of urbanisation by careful design at the house and street scale, its focus has largely been on managing and re-using the runoff (stormwater and wastewater) component of the water balance. Much less attention has been paid to the role of urban evapotranspiration (ET) by urban hydrologists, even though this it is often the biggest output in the water balance. Evapotranspiration is the process that links the movement of water through a landscape with the local climate, with the process using energy that would otherwise contribute to elevated air temperatures. This passive control of the local climate via urban vegetation and ET has a direct influence on quantities of energy used in space heating and cooling through the role of urban ET and also because trees provide shade and shelter.This link between the urban water and energy balances, and microclimate, is demonstrated by considering the following simplified expressions for i) the urban water balance:P + I = ET + D + Delta S (1)where the inputs are: P = precipitation; I = piped water supply (for external and internal uses); and the outputs are: ET = urban evapotranspiration; D = stormwater and wastewater; Delta S = change in stored water on and within the surface materials; and ii) the urban energy balance:Q* + Q(E) = Q(H) + Q(E) + Delta Q(S) (2)where the energy inputs and outputs are: Q* = net all-wave radiation; Q(F) = anthropogenic energy sources (space heating, cooling etc.); Q(E) = energy used to evaporate the water flux E; Q(H) and Delta Q(S) = energy used to heat the air, soil and built surfaces.Urban ET also contributes to reducing net greenhouse gas emissions, directly because water loss via transpiration is the consequence of the uptake of CO(2) during photosynthesis, and indirectly because reduced energy consumption reduces greenhouse gases consumed in burning fossil fuels to generate electricity. Maintaining urban greenspace via irrigation is therefore a quantifiable benefit of water use in terms of reduced energy consumption and net greenhouse gas emissions. Quantifying these benefits is critical if they are to be included in current discussions about urban water use.To address the gap in current WSUD practice, and investigate the potential to realise multiple benefits from urban vegetation, we use a calibrated urban water cycle model to quantify the impact of urbanisation and different suburban designs (layout, population, style and size of housing etc.) on the seasonal and annual urban water balance, especially ET, in an Australian city. We show that urban ET is the largest output term in the average urban water balance (almost twice the size of urban runoff) and is sustained during periods of low rainfall by the use of imported water to irrigate household gardens and larger urban parks. We show that this urban ET lowers air temperatures to reduce energy demand for cooling during peak air temperatures. The simulations demonstrate that the magnitude of urban ET can be manipulated through different suburban designs, e. g. urban consolidation reduces urban ET by about 50%, doubles the urban runoff, and increases afternoon air temperatures by about 1 degrees C. Such an increase could increase energy consumption by 3%.