A water storage cell (2) is positioned underneath a pavement (4). An upper boundary of the cell (2) is formed by a surface (6) or wearing course of the pavement (4). The remaining boundary of the cell is defined by a water-retaining layer (8) that may pen-nit infiltration of water into the surrounding ground. Means for enhancing the evaporation rate of the water in the cell are provided. As shown a ventilated pathway (20) extends between a vent (22) and a flue (24) and is surrounded by means such as a liner, suspended dished panels, absorbent mats (32) or particulate material with surface absorbency characteristics to detain water in contact with the airflow in the pathway (20). The cell (2) can be used in a SUDS system without an outfall with both permeable and impermeable pavements.