Sauerbrunn, Marhof, Natural spring in Marhof, Austria

The Erzherzog-Johann-Quelle is the main spring of a group of small springs in Sauerbrunn, in the Marhof part of Stainz, at about 500 m above sea level. Its catchment lies on the Trogbach, roughly 200 m upstream from where that stream meets the Stainzbach. The other springs are hard to find, but their outlets are marked by ochre-coloured ground caused by iron in the water.

Bronze coins from the reigns of Constantine to Arcadius (c. 292–408 AD) were found at the spring, which belonged to the Stainz monastery from the 14th century; a wooden-pipe spring is documented in 1632. Archduke Johann acquired it in 1840 with the estate of the dissolved monastery, but it was his son Franz Graf von Meran who had it refitted in 1875 with a marble rim, and a wooden pavilion followed in 1878. A small spa building opened in 1883, and from 1882 the water was bottled and sold.

The spring takes its name from Archduke Johann, who acquired it in 1840 with the estate of Stainz Abbey; it has no link to John the Baptist. From 1883 the site ran as a spa with baths and drinking cures, and water was bottled until 1978. A legend holds that the water protected Stainz residents from the plague.

Water can be collected year-round at no cost from the spring outlet, so visitors should bring containers. The basins are also freely accessible and require only appropriate clothing for wading.

The water leaves reddish deposits around the spring outlet, a visible sign of its high iron content. These colored traces form when minerals in the water react with air and remain as natural staining.