| Hardtbach | |
| Mouth Coordinates: | 50.7625°N 7.0823°W |
| Subdivision Type1: | Country |
| Subdivision Type2: | State |
| Length Km: | 15.0 |
Hardtbach (also: Rheindorfer Bach, Dransdorfer Bach, Alte Bach) is a river of North Rhine-Westphalia, Germany. It is a left tributary of the Rhine near Bonn.