In the present endeavor, a conventional single-slope solar still has been modified to improve its performance by coupling it with a novel nanofluid-based volumetric absorption solar collector (NBVASC). A low-cost and thermally stable nanofluid (prepared by dispersing functionalized carbon soot nanoparticles extracted from used engine oil into paraffin oil) having high solar weighted absorptivity has been employed to volumetrically absorb the incident solar energy. This additional absorbed solar energy is provided to the solar still by circulating a heat transfer fluid in a closed loop through serpentine type heat exchangers placed inside the NBVASC and the solar still. The experiments were performed from May to July 2020, and the results of the experiments conducted on May 25 and June 9, 2020, are reported. Extensive on-sun experiments reveal that coupling NBVASC to the conventional still could lead to substantial performance enhancements—distillate productivity, thermal efficiency, and night distillate improved by 75.3%, 66.9%, and 33.9%, respectively. More importantly, solar still coupled to NBVASC was found to perform better at an optimum nanoparticle concentration of 1.25 mlL−1 (20.75% higher distillate productivity) than the solar still coupled to a surface absorption-based collector (with paraffin oil as the working fluid)—truly establishing the benefits of volumetric absorption over surface absorption under the given set of conditions. Overall, the present study represents a noteworthy step forward in realizing efficient solar energy-driven desalination systems for remote underdeveloped areas.