This review explores water-based passive cooling strategies as sustainable solutions for reducing heat gain through building envelopes in hot arid climates. Addressing both transparent and opaque envelope systems, the study examines how water's thermal and optical properties can be leveraged for enhanced thermal regulation. Inspired by biomimicry, it highlights nature-based techniques for water harvesting and surface cooling-such as fog collection and evaporative behaviors observed in arid-dwelling organisms. Key applications include water films on glazed fa & ccedil;ades, water-filled double glazing, fa & ccedil;ade spray systems, integrated rooftop ponds, and embodied water within walls and slabs to improve thermal mass and heat absorption. These strategies are evaluated for their potential to enhance indoor comfort, reduce mechanical cooling demand, and align with local climatic conditions. The review synthesizes existing knowledge, discusses system limitations related to efficiency, water consumption, and maintenance, and identifies key challenges and potential solutions for researchers, policymakers, and industry practitioners. By positioning water as a multifunctional design medium, this work aims to contribute to the development of low-energy, climate-resilient architecture aligned with global sustainability goals.