Implementing real water saving measures in irrigated agriculture is only possible if all the components of the current water balance are clearly understood. Although measurement of all these components is infeasible on a spatial and temporal scale, hydrological simulation models can fill the gap between measured and required data. to obtain all terms of the water balance for the Gediz Basin in western Turkey, simulation modeling was performed at three different scales: field, irrigation-scheme, and basin. These water balance numbers were used to calculate the productivity of water (PW) at the three scales. The four performance indicators considered were: PW irrigated (yield/irrigation), PW inflow (yield/net inflow), PW depleted (yield/depletion), and PW process (yield/process depletion), all expressed in kg (yield) per M3 water. Of the two cotton fields evaluated at the field scale, the more upstream field performed better than the downstream field. This was partly attributable to the difference in climatic conditions, but was mainly due to the location of the two fields: upstream and downstream. At the irrigation-scheme scale, PW irrigated was higher than at the individual cotton field scale, since non- irrigated crops were also included. Other PW values were lower than those at the cotton field scale, since crops more sensitive to drought were also found in the irrigated areas. Because large areas of the basin were concealed with less productive land cover, the basin scale PWs were lower than those at the irrigation-scheme and field scales. The report concludes that performance indicators are useful ways of representing water dynamics, and that it is important to consider all the spatial scales at the appropriate scale of detail. (Author abstract, modified)