Hydroponically grown lettuce has been a staple crop in CEA (Controlled environment agriculture) facilities for decades, however, there is still knowledge to be discovered on how to grow most optimally. There are a handful of system designs that have been optimized for growing lettuce and other greens such as NFT (Nutrient Film Technique), DWC (Deep Water Culture), and aeroponics. Many of the parameters that differ among the types of hydroponic systems are well understood in regard to growing lettuce. However, there seems to be little information on the effect of changes in water depth in nutrient film technique (NFT) channels and how that may affect plant growth. As suggested by the name, NFT systems employ a thin layer of recirculating nutrient solution in which the root plants grow. However, it is unknown whether a deeper water column in the same channels will affect yield. A deeper column may also help mitigate detrimental effects of temporary pump/power outages. The objective of this study was to discern whether changes in water depth in NFT channels would have an effect on the growth of lettuce (Lactuca sativa), ’Rex’. Lettuce was grown in a greenhouse in prefabricated plastic channels at four different water depths (0.3 cm [control, standard NFT water depth], 0.5 cm, 1.0 cm, 2.0 cm). The system was designed so that the water depth was the main variable between treatment groups. Over the course of three crop cycles, information on plant biomass (fresh and dry weights of the roots and shoots, root-to-shoot ratio) and morphological cylindrical volume was determined. Changes in water depth led to significant changes in dry weight, but not in fresh weights. Specifically, mean root dry mass from the 0.3 cm group was significantly greater (from 5.9% to 6.2% increases) than the other treatments. Mean dry weight of lettuce heads in the 0.3 cm was also significantly higher (3.1% increase) than the 2.0 cm treatment. In regard to cylindrical volume, the 0.3 cm control treatment had an overall lower mean volume (12.4% decrease) compared with the 2.0 cm depth treatment. There were no significant differences between treatment for fresh weights of the roots or shoots or the root-to-shoot ratio. Overall, based on fresh weight, a deeper water column could be employed in NFT systems to mitigate temporary power outages, to save on energy costs, or take advantage of other design benefits; though more research should test these notions in a commercial facility.