In order to test the current recommendation for reservoir safety that a snowmelt of 42 mm/day can be used throughout the UK, calculations of hourly snowmelt rates were made for hourly weather reporting stations in the UK. These data were analysed to give annual maximum melt totals for periods of 3, 6, 9, 12, 18, 24, 48, 72, 120 and 168 hours. Supplementary data from high altitude climate stations allowed further 24-hour melts to be calculated. The annual maxima were entered into an extreme value type one (Gumbel) analysis and estimates of the melt with return periods of 5, 20 and 50 years were made for the durations of 3, 6, etc. hours. An estimate of the return period of a 24-hour melt of 42 mm was made for the sites. These return periods were below 10 years in some high altitude Pennine and Scottish sites, but in excess of 1000 years at low altitude in England. The 24-hour melt with 5 year return period at the sites was related to altitude, northing, mean January temperature and windspeed in linear regressions which permit a calculation of snowmelt at any point in the UK.