A common bath product is named after a well whose water the cows refused to drink. The salt is magnesium sulfate, and its everyday name points to a small town in Surrey.
The usual story begins in 1618. In a dry summer, a man named Henry Wicker found water for his cattle on Epsom Common, about half a mile from the town. The cattle would not drink it, because of its mineral taste. That account, written about forty years later, was quoted in James Thorne's 1876 handbook to the area. The water was first used on sores and wounds, and later drunk as a medicine.
Etymonline adds a wrinkle: it says the water's medicinal properties were discovered in Elizabethan times, before the 1618 well. Either way, the well and its water were soon named for Epsom.
Epsom became a spa town. By the middle of the 17th century, Epsom water was known as far away as continental Europe. A second well was dug nearer the village center, and that site became widely known as Epsom Spa.
Science gave the salt its fame. In 1695 Dr Nehemiah Grew published a study of the water's composition. That work helped establish Epsom salts as a medical remedy in their own right, and local historians credit it with fixing the name.
The original wells did not last. Thorne reports that they were neglected by the end of the 18th century, and the old well buildings were pulled down in 1804. Etymonline dates "Epsom salts" in English to 1770, by which time the name was attached to the substance itself, not the spring.
The salt also occurs naturally as a mineral, epsomite, which was described systematically in 1806. In fibrous form it has also been called "cave cotton."
The place name is older than any of this. Etymonline records it around 973 as Ebbesham, "Ebbi's homestead," after an Anglo-Saxon whose identity is forgotten.
Epsom has a second claim to fame. The Derby, first run in 1780 and named after the 12th Earl of Derby, is run at Epsom. So one town lent its name to a laxative salt and hosts a horse race named after somebody else.