| Armuthsbach | |
| Subdivision Type1: | Country |
| Subdivision Name1: | Germany |
| Subdivision Type2: | States |
| Subdivision Name2: | North Rhine-Westfalia and Rhineland-Palatinate |
| Subdivision Type3: | Reference no. |
| Subdivision Name3: | DE: 271856 |
| Length: | 18.372 km |
| Source1 Location: | South of Tondorf |
| Source1 Elevation: | ca. |
| Mouth Location: | West of Schuld into the Ahr |
| Mouth Elevation: | ca. |
| Basin Size: | 60.526 km2 |
| Custom Label: | References |
| Extra: | Gorse blooms in the Armuthsbach valley between Pitscheid and Wennefeldermühle |
The Armuthsbach is an 18.4-kilometre-long, orographically left-hand tributary of the Ahr in the German states of North Rhine-Westphalia and Rhineland-Palatinate.
The Armuthsbach rises about 1.5 km southwest of Tondorf at a height of . Its spring lies on the territory of Blankenheim. Flowing in a mainly easterly direction the Armuthsbach passes through the village of Rohr. Below the settlement the stream reaches the state border with Rhineland-Palatinate. As it continues to its mouth, there are no further villages along its course. About 400 metres north of the stream is Hümmel, about 900 metres south is Wershofen. About 800 metres west of Schuld the Armuthsbach empties into the Ahr from the left at an elevation of .
The Armuthsbach flows through the North Rhine-Westphalian nature reserve of the Armuthsbach and Tributaries (Armuthsbach und Nebenbäche).
The stream descends through 286 metres and has an average riverbed gradient of 15.5 ‰. Its catchment area covers 60.526 km2 and its waters drain via the Ahr and Rhine into the North Sea.
The most important tributary of the Armuthsbach is the 7.7-km-long Buchholz Bach. The following table lists the tributaries of the Armuthsbachs as they are recorded in the waterbody index of the state of North Rhine-Westphalia.
| Name | Position [km] | Bank | Length [km] | Catchment area [km²] | Mouth elevation [m above NHN] | DGKZ | |
|---|---|---|---|---|---|---|---|
| Derchbach | 16.588 | left | 1.1 | 1.899 | 472 | 271856 112 | |
| Mühlenbach | 16.339 | left | 1.6 | 467 | 271856 114 | ||
| Werthsbach | 14,747 | right | 2,5 | 441 | 271856 116 | ||
| Weierbach | 13.490 | right | 1.9 | 419 | 271856 118 | ||
| N.N. | 12.624 | right | 1.0 | 408 | 271856 1192 | ||
| Wellbach | 12.499 | left | 3.1 | 2.133 | 407 | 271856 12 | |
| Borner Bach | 11.041 | left | 2.5 | 393 | 271856 132 | ||
| Bröhlinger Bach | 9.238 | left | 3.3 | 3.987 | 370 | 271856 14 | |
| N.N. | 8.013 | left | 1.1 | 351 | 271856 152 | ||
| Mühlenseifen | 5.854 | left | 1.6 | 1.040 | 330 | 271856 16 | |
| Brömmersbach | 2.796 | left | 5.6 | 8.825 | 283 | 271856 18 | |
| Buchholz Bach | 1.929 | left | 7.7 | 17.676 | 269 | 271856 2 | |
| Rupperather Bach | 1.505 | left | 1.6 | 266 | 271856 92 |