The paper investigates the impact of employing in-field rainwater harvesting (IRWH) production techniques on household food security for communal farmers in Thaba Nchu, by estimating the minimum area of land that a representative household needs to cultivate in order to meet its requirements. First, using a poverty datum line for South Africa, annual income required by an average household for food and other basic necessities (shelter and clothes) is calculated, given a specific level of non-farm income for a typical household in the study area. Second, the caloric requirement for an average household's is estimated by using the daily caloric requirement of each member of the household. The household uses its income from non-farm sources to purchase food and where necessary supplemented with income from the sale of non-food agricultural production. In both cases minimum farm size is influenced by output levels and by profitability of crop production under IRWH techniques.