Discrete total alkalinity data for 13 sites in the Humber catchment sampled within the period 1993 to 1997 and 1996 to 1997 and for 3 sites from the Tweed catchment over the period 1994 to 1997, as part of the Land Ocean Interaction Study project (LOIS). Sites were sampled at regular weekly intervals and more intermittently during high flows (on average an extra sampling once a month per site). Samples were analysed on day of collection or on arrival at the laboratory using a Metrohm 702 Titrino autosampler.