Among potential solutions to global water scarcity, thermal desalination is a flexible choice for water treatment, given its key advantages in robustness and limited salinity dependence. Light can power thermal desalination by dissipating electromagnetic energy into heat. Solar-driven photothermal desalination (SDPD) can lead to decentralized water purification, improving accessibility and reducing the environmental impact over conventional, heavy infrastructure-based desalination practices like reverse osmosis. Unfortunately, today’s best decentralizable SDPD technologies barely surpass 10% of the thermodynamic limit for thermal desalination. Furthermore, there is limited consensus on how to best evaluate and compare the efficiency of diverse solar-driven systems, particularly with respect to their day-long performance under natural, time-varying intensity. Recently, we proposed a generalized approach for achieving efficient, scalable, and day-long SDPD. Instead of optimizing individual components like solar absorbers and evaporators, our approach emphasizes the critical transfers of power underpinning the entire thermal desalination process. In particular, the minimization of environmental losses and maximization of heat recovery depend on each other, and their combination is paramount in bolstering the performance of real-world practical systems. Guided by our approach, we have determined that SDPD systems of a specific size and input salinity operate most efficiently at a specific optimal input power, a previously understudied fact with major implications on the day-long operation of modular networks of individual systems. By focusing on optimizing system-wide thermal energy recovery, loss mitigation and exploiting dynamic energy recovery schemes that can be tuned adaptively for time-varying input power, highly efficient, cost-effective systems can be designed to best take advantage of available light.