The lack of hydrologic databases for basins in the irrigation system hinders the rehabilitation of irrigation systems. The dry zone of Sri Lanka is an area in which information on hydrology and water use is inadequate. Therefore this report provides a methodology to plan the rehabilitation of small tanks in this area. This methodology was field-tested in Sri Lanka’s dry zone and can be applied in other countries with similar conditions. The report first provides information to show the need for a basin-wide context when planning irrigation system rehabilitation. It looks at the room for improvement in the tank irrigation systems in the dry zone. The report makes a compelling case regarding the basic elements of the methodology and the need to select specific areas of work. This method uses data collected from farmers, topographic maps and rapid assessments. The report provides an assessment of tank cascade hydrology and provides rehabilitation proposals. There is also a report on the Makichchawa Cascade, where this methodology was applied. Supplemented with facts and figures, this report shows how effective this methodology will be in the rehabilitation of small tanks in cascades.