African Crop Science Conference Proceedings 2013, Vol. 11: 835 - 843Crop production in semi-arid Sub-Saharan Africa (SSA) is limited by over-reliance on rainfall, which is erratic and inadequate. Rainwater conservation and irrigation are needed to avert drought effects and dry spells, and extend crop production activities to dry seasons. A study was conducted from 2011 to 2013 at Ukwe area in Malawi, to determine the size of seasonal open surface reservoir and crop field in relation to catchment characteristics among smallholder farming communities, using beans as a case study crop. There is positive linear relationship between seasonal harvested watershed runoff and rainfall (over 75%). Based on the catchment characteristics and crop water requirement, catchment/cultivated area ratio was 2.1. Harvested runoff water is linearly related to seasonal rainfall amount. About 6000 m3 of water was required to irrigate a hectare of beans. Total volume harvested was estimated to support six-fold the current field area at bean water productivity of 0.7 g L-1. It is possible to determine dry season bean water productivity based on integrated effects of catchment characteristics, runoff water reservoir capacities and irrigation water requirement.