We often go here for a walk and what can do you on Bank Holidays, read up a bit on it's history.
The dam holding the Lower Lliw reservoir was completed in 1867. However it devolped a leak, so was kept at a low level. That was until 1979 when it was rebuilt 112 years after first being constructed. I'm sure I've read they started it in 1862 so spent five years building it for it not to work. Phew bet the guy in charge of that took some stick!
The reservoir originally supplied water to Swansea area, but now after being treated at the nearby Felindre Water Works, the water is pumped all over South Wales.