This paper reports on an investigation into the effects of the shape of concrete paving blocks used in permeable pavements. It describes a series of hydraulic performance tests on blocks with different drainage slot geometries, in order to determine their influence on infiltration capacity. Paving samples were tested in a purpose-designed laboratory rig consisting of a variable-gradient testing frame, rain simulator and water-collecting chambers. The apparatus allowed for slope variations and two inputs of water: input runoff and direct rainfall over the surface. Four differently shaped slotted concrete blocks were tested under three different clogging states and four gradients. The results obtained lead to initial conclusions about the influence of block geometry on the hydraulic performance of paving which have implications for pavement design.