The constancy of abstracted water throughout the year reflects the absence of seasonal variations on the discharge of the major springs and groups of springs that feed the water supply system, accounting for about 54% of the annual volume (Fig. 3): Ribeira da Praia (30 springs), accounting for 19.4% of the water supply, Galeria de Mina, Lourinhos I and II (six discharges), Grota do Lanço (10 springs) and Janela do Inferno (3 springs). In the winter period, when the overall spring discharge for the system is slightly higher, groundwater abstraction in the drilled wells is negligible (Fig. 3).