Retaining abundant flood water and later using it as crop irrigation water is an issue for the flood-prone area in the Mekong Delta of Viet Nam. The present study aimed to determine an appropriate rice-based upland crop production practice with high water use efficiency and hence the feasibility of retaining  flood water for agricultural use in the flood area in the Mekong Delta. On-farm studies were carried out in Chau Phu district of An Giang province from January 2012 to July 2015. Chilli, maize, rice were used as the proxy crops. Crop irrigation water quantity was monitored, and crop yields  and economic inputs and outputs were recorded. Results showed that maize or chilli grown on the paddy field were more water-efficient than rice cropping alone. Double maize and chilli cropping, and rotational rice and maize or chilli cropping required an irrigation water volume of 3,341 m³/ha and 3,686 m³/ha, respectively, compared to 4,289 m³/ha for the commonly-applied double rice cropping. For financial water use efficiency, each cubic meter of water used for crop irrigation yielded a net value of output of 10,950 $VN with double maize and chilli cropping, 6,370 $VN with rotational rice and maize or chilli and 2,790 $VN with double rice cropping practice. These results need to be validated with more farmers’ fields to evaluate the feasibility of the promising crop production systems in larger scale.