The carbonic acid, iron, and sulfur-containing spring on the right bank of the Waldnaab River, directly on the hiking trail between Kammerwagen and Butterfaß south of Falkenberg in the wild and romantic Waldnaab Valley, is called a "Sauerbrunnen" (sour spring). It is a "sour spring" (a narrowing spring) that is probably attributed to the reverberations of Tertiary volcanism in northeastern Bavaria.
The "sour spring" has been known for centuries. Today, the enclosed spring is easily accessible via a few steps and has been attractively maintained. The water is said to have certain healing properties, possibly due to its iron content. However, since no current studies (e.g., regarding bacterial counts) are available, one should refrain from trying it for oneself.
Carbonic acid springs (sour springs) are noticeably more frequent in northeastern Bavaria near Tertiary basalt deposits. Examples include the springs of Kondrau, Wiesau, and also the West Bohemian spa triangle. The acid springs emerging in the Egergraben area are associated with this Tertiary volcanism. The acid spring is likely the southernmost acid spring in this system.
The water from the acid spring is not considered "palatable" by most people. The reason for this is mainly its iron content, which at a few mg/l is several times higher than the drinking water limit (0.2 mg/l). The spring's steady flow, with its pencil-thick water jet, is a few liters per minute. The spring lies about 2 meters above the level of the Waldnaab River at approximately 457 meters above sea level.