This study is focused on a climate data integrity to improve water quality assessment due to the social development projects. The study is in an attempt to calculate both extreme ranges of weather data measurements and partly provide means to assess qualification of data which fall within the extremes at the 23 meteorological weather stations. Generally speaking, maximum temperature, minimum temperature, relative humidity, dew point temperature are in the range of reasonable accuracy. However, there found some outliers of the brightness sunshine hours in Cheonan station. Also some years in Gwangju, Seoul, Wonju, Busan, and Jeju never reach to their upper limit and perhaps the calibration of the equipment is doubtful. The users need to take cautions in using the brightness sunshine hour data in preparation of water resources planning and management by estimating evapotranspiration and river discharge, and/or growth rate of the algae (phytoplankton).