A good way to increase separation is to light the water separately from the background. Use a large, diffused flash—such as a softbox or a flash fired through a diffuser—and aim it at the water from the front or from behind, depending on the look you want. Then reduce the ambient exposure so the bushes go darker. This increases contrast and makes the water stand out more clearly.

Your wider aperture already helps by softening the background, but the biggest improvement from the advice given is controlling the light ratio: brighter light on the water, less light on the foliage. Diffused flash is preferable because it gives you softer, more controllable highlights on the water.