A simple, low-dose, durable, and carbon nanotube-based floating solar still (CNTs-FSS) has been prepared for seawater desalination based on interfacial solar heating. The CNTs-FSS is composed of a surface layer of CNTs to absorb solar light, a thermal barrier layer of polyurethane sponge (PUS) to avoid the heat transfer into the underneath bulk water, and a water transport channel of air-laid paper to deliver sufficient water to the CNT layer. The water evaporation efficiency (k) of the CNTs-FSS can be optimized by tuning the thickness of the CNT layer and the PUS layer. The optimized CNT dose is only 4 g/m2, far less than that of other reported carbon-based photothermal materials. The k values of the CNTs-FSS are 0.88, 1.58, and 4.64 kg/m2·h under 1, 2, and 4 sun irradiance, respectively, which are correspondingly 2.8, 3.4, and 5.3 times higher than that of the control case of pure water. The excellent durability of the CNTs-FSS has been proven by monitoring the water evaporation efficiency during at least 20 cycles of use within 30 days. Finally, we have demonstrated that the organic and inorganic contaminants in condensed freshwater can be reduced well by the CNTs-FSS.