1832, 1849 and 1854 saw cholera outbreaks in Merthyr. This caused the laying of a pipe from Dolygaer on the Taff Fechan to Penybryn in the town. A reservoir (Pen-twyn Reservoir, later Taff Fechan Reservoir, later Pentwyn Reservoir, nprn 402612) was built between 1858 and 1862, the dam at approximately SO 055145. The then-untreated water fed eleven standpipes and the ironworks, steam pumping being used. By 1880 increased demand led to Neuadd Reservoir, later Lower Neuadd Reservoir (nprn 411001), being opened. This, at 430m above sea level meant that Dowlais, Pant, Quakers Yard and Treharris could be supplied without pumping. 1902 saw Upper Neuadd Reservoir (nprn 411002) at 457m asl completed, with Cwmbargoed, Bedlinog, Abercynon, Merthyr Vale and high Treharris supplied. The mushrooming of Barry and the needs of Rhymney and Pontypridd added to those needs already existing and Taff Fechan Reservoir, later Pontsticill Reservoir (nprn 402075), planned in 1910 but delayed by the First World War, was opened in 1927. The combined recipients had by then formed the Taff Fechan Water Supply Board.
(Source: A Guide to the Industrial Archaeology of South East Wales, AIA, 2003)
The reservoir is retained by an earth dam at its southern end, revetted with pitched stone on its inner face. There is an outflow in the form of a circular convex-sided funnel adjacent to the dam, with concrete ribs and a masonry lining. Nearby stands a Gothic-style rock-faced octagonal valve tower with a steeply-pitched copper-clad roof, accessed by a steel lattice bridge from the end of the dam.
B.A.Malaws, RCAHMW, 09 June 2011.