Cantref Reservoir is the middle of the three reservoirs in the Taff Fawr valley in Wales. It is owned by Welsh Water. It is located in the Brecon Beacons National Park, mostly in the Powys unitary authority area and within the historic county boundaries of Breconshire. Part of the south west corner is in the Rhondda Cynon Taff unitary authority area.
Rhondda Cynon Raff is a borough in South Wales. 
The passage doesn't specifically say the location of Rhondda Cynon Raff, it is in Wales and is in the south west corner and the AI can not link the two