Non-transpiration water loss is often neglected when evaluating water use efficiency (WUE) of precision irrigation system, due to the difficulties in determining water loss from the root zone. The objective of this study is to investigate the feasibility of a new water saving approach by controlling soil water retention around root zone during the plant growth. We grew two tomato cultivars (Anemo, Japanese variety) in an environmental controlled growth chamber, with previously oven dried and sieved red soil as substrate for cultivation. In order to investigate the water productivity at a minimal irrigation level for the tomato growth. The procedure involved supply a meager amount of water (10ml) from a point water source to the plant root zone when the plant started to wilt. The water supply was repeated several times (4-7 times) a day. We confirmed plant growth from seedling to the first fruit maturing under this extreme condition.  There were no evaporation and deep percolation losses due to the boundary separated the wet and dry soil was visually observed. Plant increased biomass in response to the water applied in the water retention zone. The fruits weight, dry shoot and root biomass were used to analyze the WUE. As a result, the total water supply was 1/10 less than conventional irrigation while WUE was about 1/4 lower. The approach developed in this study aims to be used to develop new standard for comparison of the water saving degree of precision irrigation system.