| Ruhlander Schwarzwasser | |
| Subdivision Type1: | Country |
| Subdivision Name1: | Germany |
| Subdivision Type2: | States |
| Subdivision Name2: | Saxony and Brandenburg |
| Subdivision Type3: | Reference no. |
| Subdivision Name3: | DE: 53818 |
| Source1 Location: | Source region: in the Bernsdorf municipal forest near Heide, part of Wiednitz |
| Source1 Coordinates: | 51.3968°N 14.057°W |
| Mouth Location: | near Ruhland into the Black Elster |
| Mouth Coordinates: | 51.4638°N 13.8156°W |
| River System: | Elbe |
| Progression: | Black Elster → Elbe → North Sea |
| Basin Size: | 269 km² |
| Tributaries Left: | Saleskbach |
| Custom Label: | References |
The Ruhlander Schwarzwasser is a left-hand tributary of the Black Elster in the east German states of Brandenburg and Saxony.
It rises in the Bernsdorf Forest (Bernsdorfer Gemeindewald) near, a village in the borough of Wiednitz (today part of Bernsdorf). As it makes its way westwards, this small river flows partly through the state of Brandenburg and partly through Saxony. In the Ruhland Heath (Ruhlander Heide) it forms the boundary between the two states. There it is also joined from the left by the Saleskbach, which comes from the heath villages of, and .
The Schwarzwasser then flows northwards through and . It discharges into the Schwarze Elster near the town of Ruhland.
In Arnsdorf the Sieggraben dyke branches off on the left. It also enters the Black Elster, below Ruhland.