Sri Lanka is highly popular for its advanced irrigation systems dating back to the third century BC. Tank cascade system is a unique intervention to store water in a series of interconnected tanks during the rainy season and to use it during the drought in the dry zone of Sri Lanka. At present, ancient knowledge and wisdom have been used with advanced modifications for wastewater treatment. Sewage collection, treatment, and disposal/reuse strategy has been developed based on hybrid solutions. The floating wetlands are a recent intervention on wastewater reclamation. Application of floating wetlands was tested in pilot studies at the University of Peradeniya and implemented at Kandy Lake as a pioneering field scale application in the country. The learning from the constructed floating wetland in Kandy Lake was extended to Kurunegala Lake. The effectiveness of the floating wetland is assessed with reference to technical, social, economic, and policy and governance. The assessment is, in principle, based on a matrix as impact and existence. There is substantial number of parameters used in each subcategory in order to ensure a detailed and unbiased assessment ensuring sustainability. This exercise is very helpful to sustain, upscale, and replicate nature-based solutions in Sri Lanka.