WATER BALANCE A TOOL FOR PLANNING IN NORTHWAEST OF STATE OF SÃO PAULOKnowing the availability of the water on the soil for the future planning is the foundation for executing its rational use. Then, this project had as an objective to elaborate the monthly water balance for the region of Marinópolis, worthwest of the state of São Paulo. The water balance was determined using the Thorthwaite and Mather (1955) method, starting from the data obtained by Weather Station operated by the Hydraulics and Irrigation Division from UNESP Ilha Solteira. The year average precipitation is 1.111 mm and the potential evapotranspiration from 1.421 mm per year. Considering a Available Water Capacity (AWC) from 40 mm, the water balance resulted in eight months of water deficiency on the soil (april to november), with total accumulated of 490 mm and the surplus occurred in the months of december to march with 179 mm, concluding that it would be high rick with the cultivation without the use of systems of irrigation that must be projected to attend a demand between 3,9 and 4,6 mm per day.