This paper presents the traditional design principles of the suranga water-harvesting system found in an area of semicritical groundwater scarcity in the Dakshin Kannada district of Karnataka and Kasaragod district in the state of Kerala, India. This region is situated in the foothills of the Western Ghats of southern India. Data were derived from a mixed-methods approach that analyzed the structure, technology, governance, organization, and hydrological principles of a little-known and little-understood irrigation system. The main body of this work came from a survey of 215 households that identified 700 suranga over a core area of ∼6850 km². The total number when added to other inventories puts the figure at closer to 3000 suranga overall. The suranga system was identified, relative to other traditional water-harvesting systems in mountains, as a gallery filtration tunnel system that is exclusively constructed in laterite substrate. These laterites have a sound internal structure that does not require support structures. Many suranga are found in cascading hydrological networks on more extensive farm units linked to a storage network of small ponds and check dams. The main sources of water come from either perched or shallow aquifer groundwaters that are variable in their discharge rates, such that some systems are perennial, and others are seasonal. Discharges from suranga range from 0.005 m³/s in the dry season to 0.1 m³/s in the period immediately after monsoon. Organizational principles are simple, and nearly all systems are privately owned. Access to water is usually private with just a few usufruct arrangements prevalent that come in the form of the sharing of water. The immediate future of suranga is under threat from unregulated bore well construction and use.