Water supply system. NW end commences at given NGR, adjacent to the waterfalls above Nannerth-Ffrwd, where there is a concrete sluice on the stream. The sluice diverts water into a concrete cistern whose interior contains stop-cocks, an overflow, and a slate slab sluice-gate within three chambers. To the SE of the cistern a terrace runs across the slope, defining the course of a cast-iron pipeline, whose course is lost to the W of Fergwm. Discussions with the owner of Nannerth-Ffrwd suggest that it may have supplied Rhayader. (R Hankinson, CPAT, 04/12/2002)