Monthly consumptive use of water (CU, mm) by rice was estimated with modified Blaney-Criddle model, Hackbarfts computer program and available climatic data in the semiarid south coast (Lajas) and humid north coast (Arecibo) of Puerto Rico. Twelve planting dates and three crop lengths of 90, 105 and 120 days were considered. For 120 days and 12 planting dates, total consumptive use varied from 442 to 589 mm at Arecibo, compared with 428 to 579 mm at Lajas. Average total CU (mm) was 392 for 90 days, 458 for 105 days, 514 for 120 days at Arecibo, compared with 382 for 90 days, 447 for 105 days and 502 for 120 days at Lajas. Daily CU (mm/day) range was 4.3 to 4.4 at Arecibo, compared with 4.2 to 4.3 at Lajas.