Plenty of testaments to the well’s healing properties can be found in Hunt’s ‘Popular Romances of the West of England’ (1886), online at the sacred-texts archive, here:
sacred-texts.com/neu/eng/prwe/prwe148.htm
You can also find out when you will be married:
In Madron Well--and, I have no doubt, in many others--may be found frequently the pins which have been dropped by maidens desirous of knowing “when they were to be married.” I once witnessed the whole ceremony performed by a group of beautiful girls, who had walked on a May morning from Penzance. Two pieces of straw, about an inch long each, were crossed and the pin run through them. This cross was then dropped into the water, and the rising bubbles carefully counted, as they marked the number of years which would pass ere the arrlval of the happy day.