Humidification-dehumidification (HDH) desalination technology is one such technology (based on thermal desalination technology) which has been found to be ideal for small scale water productions (1-100 m3/day). It requires less maintenance and can be combined with renewable energy sources such as solar or geothermal due to lower temperature operation. In this paper, nanofluid-based direct absorption solar collector (DASC) has been coupled with the one of the versions of HDH desalination system (closed air open water - CAOW) with the help of a counter-flow heat exchanger. These collectors (DASCs) have high thermal efficiency (10% higher) as compared to conventional surface absorption based collectors. Numerical model is prepared for a closed air open water HDH system, working together with a direct absorption solar collector. The aim of the present study is to evaluate the thermal performance of the system in terms of gained output ratio (GOR) against the various influencing parameters related to the solar collector such as, height (H) and length (L) of the collector, nanoparticle volume fraction (fv), and incident solar radiation on the collector (q) and the effect of the aforementioned parameters on the collector outlet temperature (Tout) have also been analyzed in detail. Solar weighted absorptivity (Sab) for different nanofluids has also been calculated which helps in choosing the suitable nanoparticle material for preparing the nanofluid. The gained output ratio of the proposed system was found to be around 16% higher, compared to conventional CAOW-HDH desalination systems under certain operating conditions. Finally, the model proposed in this study has been validated with the data available in literature. Copyright © 2018 ASME.