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Management of water content and nutrient status during space flight is a critical element for successful plant production systems. Our objectives were to determine if dual-probe heat-pulse (DPHP) sensors could improve water content determination accuracy over single-probe heat-pulse (SPHP) sensors, and to test a design using coupled heat-pulse and direct-current electrical conductivity sensors, paired as a 4-electrode array. The DPHP predicted water content correlated well with independently measured water contents based on a physically-derived one-point calibration model. SPHP water content prediction was comparable to the dual-probe sensors when using an empirical relationship. Pooled regression analysis showed that water content for both sensors was accurate with a root-mean square error of 0.02 cm3 cm−3. Electrical conductivity was measured in both saturated flow-through and static unsaturated measurements.