Does former coal land of low acid-generating potential impact significantly on water quality in their immediate environment? This chapter explores the evidence from Southeast Wales using data collected on an array of reclaimed opencast coal-lands in a largely post-industrial area where river quality has now improved after many decades of severe pollution associated with under-regulated coalmining and metal working during the 19^th and 20^th centuries. Results show that, because of compacted layers in the immediate subsurface, former opencast coal land converts incident rainfall to runoff very quickly through a very thin active layer and may contribute to increased flood peaks in affected catchments. Opencast spoils are locally contaminated with metals, especially in the absence of vegetation, but high rainfall and rapid throughflow ensures that the offsite impacts are small because of dilution. The main impact of former opencast sites on river water quality is likely to come through diffuse pollution from the zone of aeration and water table fluctuation zone in the body of the buried spoils. Although this zone is mainly detached from the surface hydrological system and deprived of rainwater infiltration by the impermeability of the surface layers on these sites, the lateral percolation of groundwater from offsite through the crushed rocks of the spoil is very likely to pick up metals from chemically active inclusions, often former deep-mine spoils, within the opencast mine fill. However, the effect on river water quality in southeast Wales is not great but may involve slightly higher flood peaks, elevated levels of iron and slightly elevated levels of lead, perhaps arsenic, copper and zinc, as well as ammonia N, although opencast sites are only one among several possible sources for such metals, which include natural ground water and other types of industrial waste.