The aim of this paper is to quantity the annual average consumption of water in 13 public hospitals in Extremadura (Spain). An analytical study in order to reduce water demand was conducted from 2010 to 2014 in the above-mentioned hospitals. The study concluded that, in order to determine the average annual water consumption, a fixed ratio is not the appropriate tool. A parametric type related to the built surface area and/or number of beds by hospital should be used instead. The average annual consumption of cold water for human consumption (CWHC) was 262.82 m3 (102.10) per bed and 1.65 m3 (0.46) per built surface area. The mean annual consumption of domestic hot water (DHW) was 92.96 m3 (35.72) per bed and 0.59 m3 (0.18) per built surface area. The ratio between DHW and CWHC was 35.62% (5.53). The time period of greatest demand was between 12 p.m. and 6 p.m. Considering B as the number of hospital beds and S its built surface area, to calculate the average annual cold water for human consumption in a hospital, the equation 165B + 12,100 (m3) or 1.568S + 2400 (m3) should be used. Similarly, in terms of hot domestic water, the average annual consumption in m3 corresponds to either 53.65B + 5170 (m3) or 0.53S + 1400 (m3).