Solar heat helps harvest humidity: Atmospheric humidity and droplets constitute a huge freshwater resource, especially at the low relative humidity (RH) levels typical of arid environments. Water can be adsorbed by microporous materials such as zeolites, but often, making these materials release the water requires too much energy to be practical. Kim et al. used a metal-organic framework (MOF) material that has a steep increase in water uptake over a narrow RH range to harvest water, using only ambient sunlight to heat the material. They obtained 2.8 liters of water per kilogram of MOF daily at 20% RH. Science , this issue p. 430

In their comment, Bui et al . argue that the approach we described in our report is vastly inferior in efficiency to alternative off-the-shelf technologies. Their conclusion is invalid, as they compare efficiencies in completely different operating conditions. Here, using heat transfer and thermodynamics principles, we show how Bui et al .’s conclusions about the efficiencies of off-the-shelf technologies are fundamentally flawed and inaccurate for the operating conditions described in our study.

The Comment by Meunier states that the process we described in our report cannot deliver the claimed amount of liquid water in an arid climate. This statement is not valid because the parameters presented in our study were inappropriately combined to draw misguided conclusions.