On my pilgrimages I have seen many examples of holy wells not only in Wales but also in Ireland, the Isle of Man, Brittany and England. Often these holy wells are in a churchyard or close to a church. There are also a few examples where the holy well is within the church.
Natural springs clearly have great practical use as a reliable source of water, on which early settlements depended. Early churches and the small monastic communities or hermitages alongside them would have been no different.
However the water at some natural springs came to be seen as having curative or even miraculous properties. In this, there may well have been some continuity with pre-Christian pagan sites where natural springs were venerated and seen as a source of healing. However, in the early Christian centuries, some springs became associated with a particular saint. Sometimes the water was even believed to have appeared for the first time in association with the saint, such as at Holywell in Flintshire in north Wales where the beheading of St Winifred caused water to flow from the ground in the place where her head fell.
Holy wells are distinguished from simple springs in the ground by having some sort of enclosure to dignify the site and sometimes steps to give easier access. Although holy wells and their healing powers tend to associated with a pre-scientific age, many remain popular places to seek out although others have been lost to all but the most dedicated visitor.
St Bridget’s Well in the suburbs of Dublin. Numerous ribbons and other tokens have been left at this site 
Holywell in north Wales is the grandest example of a holy well. The spring, with its huge volume of water, is behind the central arch 
In Marden in Herefordshire St Ethelbert’s Well is inside the parish church, below this wooden cover in the vestry 
Holy well just outside a churchyard near Lannion in Brittany