In this study, a recoverable nanofluid was prepared with brine water in an attempt to enhance the performance of solar stills. Herein, the recoverable multiwalled carbon nanotubes (MWCNTs) nanofluids which were prepared by dispersing Fe3O4 modified MWCNTs nanoparticles in saline water with high stability and recyclability. The optical properties of magnetic MWCNTs nanofluids were thoroughly investigated and showed that prepared nanofluids could successfully ameliorate the utilization rate of solar energy to provide more heat energy for saline water evaporation. Especially, for 0.04 wt% magnetic MWCNTs nanofluids, almost 100% solar energy was absorbed when the thickness of fluid exceeded 1 cm. Furthermore, the evaporation efficiencies of nanofluids were measured under the natural solar irradiation. The evaporation efficiency was obviously enhanced with the increase of magnetic MWCNTs nanofluids concentration from 24.91% (0 wt%) to 76.65% (0.04 wt%). To better understand the enhancement mechanism of nanofluids for fresh water yield, the optical-to-heat conversion in bulk liquid was synthetically investigated and a potential enhancement mechanism for evaporation process was proposed. In summary, the advantageous performance ensured the potential of recoverable-nanofluids to broaden the application prospect of solar stills.