This technical annex describes the analytical procedures and results of a water availability assessment for the Mara River Basin using long-term historical data sets of precipitation and discharge. Objectives of this assessment were (i) to regionalize average monthly and average annual discharge data, (ii) estimate flow duration curves, (iii) set up long-term water balances for the sub-catchments within the Mara River Basin, and (iv) assess changes in the hydro-meteorological time series data sets.