While you can physically wash off some root rot by rinsing the roots with clean water, it is not enough to cure the problem. Root rot is caused by a fungal infection that affects the root system inside the soil. To treat root rot, you'll need to remove the affected plant from its pot, trim away rotting roots, and treat the remaining healthy roots with an appropriate fungicide or hydrogen peroxide solution. After treating the roots, it is crucial to repot the plant in fresh, well-draining soil.