Water is a primary control on the generation of acidic (H2SO4) effluent from commercial-scale sulphur (S0) blocks. Although clean S0 is strongly hydrophobic, microbial colonization of fracture faces and friable S0 generates localized hydrophilic conditions. Infiltration occurs preferentially along discrete fractures and in areas of friable S0. Surface evaporation rates are low (mean 0.2 mm/day), and >90% of rainfall infiltrates and rapidly drains from the blocks. A conceptual model to describe the flow and storage of water at the base of S0 blocks was developed and tested. The S0 blocks were represented as a hydrophilic equivalent porous medium, and lateral drainage through the base of the blocks was quantified using a two-dimensional numerical model. Specific yield (Sy) and saturated hydraulic conductivity (Ks) values were estimated to be ∼4%–7% and ∼1 × 10−2 m/s, respectively, by comparing measured and modelled pore-water pressure head and outflow responses to rainfall events. Given that commercial-scale S0 blocks are constructed in a similar manner worldwide, the results of this study are considered widely applicable in designing S0 block storage facilities that minimize water availability and H2SO4 production in S0 blocks.