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The objective of this research is to determine the limit of crop extractable water (CEW) for wheat grown within substrate-based nutrient delivery systems designed for spaceflight applications. The substrate compartments were constructed of clear polycarbonate and were each equipped with a bottom-situated porous tube and filled with sieved 1-2 mm Turface. Seeds were germinated, transplanted into the surface of the Turface in the substrate compartment, and a sheet of plastic was used to cover the to limit evaporation from the medias surface. The compartments were irrigated with half-strength Hoaglands nutrient solution via the porous tubes. Plant transpiration was monitored using a digital scale. Soil moisture levels were also monitored using a pressure sensors mounted to the porous tubes and heat pulse soil moisture sensors were embedded in the substrate. The plants were grown for a minimum of 45 days prior to imposing drought conditions, which were maintained until weight changes in the substrate compartments decreased to a minimum. The media from the compartments was subsequently weighed, dried, and reweighed. The average limit of CEW on a weight basis was 39.7%. The experiment was replicated five times.