Water scarcity and increasing agricultural water demand make it important to assess water supply, water productivity, and the economic implications of cropping patterns together. This study assessed water-supply conditions and compared four predefined cropping-pattern scenarios in the upstream Yamchi sprinkler irrigation network and the Ghorichay low-pressure irrigation network in the Ardabil Plain, Iran. Crop water requirements were estimated using meteorological data from the Ardabil synoptic station and CROPWAT. Water-supply adequacy was evaluated using the Agricultural Relative Irrigation Supply (ARIS) index. Physical water productivity (WP), irrigation water productivity (IWP), gross benefit per unit of irrigation water (BPD), and net benefit per unit of irrigation water (NBPD) were used to assess water productivity. Four scenarios—current cropping pattern, replacement of potato with sugar beet, replacement of potato with canola, and a 50:50 potato–canola split—were compared under deficit-irrigation and full-water-supply conditions. During the historical study period, average irrigation deficits were reported as 28% for Yamchi and 43% for Ghorichay. Mean WP was 1.52 and 2.15 kg/m³ and mean IWP was 2.16 and 4.08 kg/m³ respectively. Replacing potato with canola in Yamchi was a potentially suitable option in terms of calculated water requirement and the smaller reduction in cropped area needed under full-water-supply conditions. In Ghorichay, the existing pattern was comparatively favorable for economic water-productivity indicators under the historical prices and costs used. These results are scenario comparisons rather than the outcome of a mathematical optimization model; economic rankings should not be generalized to current conditions without updated prices and costs or sensitivity analysis.