Many of the Irish wells have folklore attached to them that the associated saint walked along, banged the ground with his crozier and the water gushed forth.
This is one: http://www.megalithomania.com/show/site/516
[this well is a few hundred metres away and appears to be a megalithic tomb: http://www.megalithomania.com/show/site/519 ]
Several Irish tombs are built on springs, Newgrange being one! There is also Shalwy in Mayo and Church Mountain in Wicklow that 'spring' to mind. Portal tombs are always near to water, usually small streams, and is such a constant in their immediate landscape that it must have meant something to the builders. The life giving source of these waters must have been special (?).