The water filter system was designed to improve dose homogeneity in Total Body Irradiation (TBI). The system is made up of a translating bed, a linear X-ray source, a vision system for body thickness assessment, a dynamically controlled water filter and a main control unit. The water filter, placed between the X-ray source and the patient, is made up of an array of 70 small water containers (cells). Water level in each cell is on-the-fly controlled, with the aim of modifying dose distribution in the transversal direction; moreover, dose delivery is modulated even in the longitudinal direction by translating the bed.