Two promising techniques to measure water uptake in a direct way were evaluated on substrate-grown truss tomato plants (Lycopersicon esculentum 'Clothilde'). The first technique, which is called the mass-balance technique, determines tomato water uptake using automated weight measurements of substrate mass and collected leachate. It was found that leachate could not be recorded appropriately in a 1-minute time interval by the tipping bucket gauges used in this study. Therefore, the tipping bucket readings had to be corrected and modified. The second technique computes the water uptake by a single tomato plant based on the thermal energy balance of a stem segment and, therefore, it is called the heat-balance technique. The stem segment was carefully selected at the base of a tomato stem so that the whole-plant water uptake could be determined. However, it was found that an independent measurement of minimum water uptake during the night was needed to correctly calculate water uptake during the whole day. As a result, the major pitfalls of the two techniques were identified. With appropriate modifications, a good correlation between the measurements was found, even during a period of imposed drought stress.