Solar-driven interfacial evaporation (SIE) has attracted extensive research for seawater desalination in recent years. Great progress has been achieved in enhancing evaporation rate and salt tolerance in open systems, but there are few studies about SIE in closed systems, let alone the differences between open and closed systems. Here, we show the differences between open and closed SIE systems using solar evaporators with tunable water transport rate. There are great differences in water evaporation rate, salt deposition behavior, surface temperature of the photothermal sheet, ambient temperature and ambient relative humidity between open and closed systems. With increasing water transport rate, the evaporation rate shows different trend in open and closed systems due to their different demand for water transport. The optimal SIE condition in the open system is inconsistent with that in the closed system. High evaporation rate can be achieved at proper water transport rate, as it determines the salt deposition area and heat loss. Also, the optimal water transport rate depends on the brine concentration. The differences between open and closed systems were further demonstrated by the outdoor practical SIE test. Thus, for harvesting more clean water, future SIE studies should focus more on closed systems.