Consumptive use of water by alfalfa grown under two phosphorus fertility levels was measured in a 3‐year study at the University of Nebraska Scotts Bluff Station, located in western Nebraska. Soil moisture to a depth of 230 cm was measured with a neutron moisture meter at the start of the growing season, after each cutting, and after the last harvest. Irrigation water was delivered to the benches through an underground pipe and measured before flood irrigation. Alfalfa used 11.4 cm water per metric ton (4.95 in/T) of 88% dry matter hay. Alfalfa used water more efficiently in early May and June than July and August. Average water use per day was 4.1 mm (0.16 in) for the first harvest, 5.6 mm (0.22 in) for the second harvest, and 5.9 mm (0.23 in) for the third harvest. Average evapotranspiration ratios for the 3‐year period were 540 for the first cuttings, 630 for the second cuttings, and 860 for the third cuttings. The average evapotranspiration ratio for the three harvests over the 3‐year period was 680. Two levels of phosphorus applied to the soil did not alter water use nor total yields of hay.