Measurements of changing water table profiles in beaches along Pegasus Bay, Canterbury, show an interchange of water between the sea and beach sand pores throughout a single semi-diurnal tidal cycle. The velocity of water escaping from the water table in response to an ebbing tide does not appear sufficient to elutriate material of silt size or larger from the beach. The low computed velocity is thought to be due to hydrostatic control, by sand dunes at the back of the beach, on water table amplitude. Fresh water and wave wash are considered important supplementary sources to that of tidal water in influencing water table profiles.