Photographing rivers, lakes, and falling water doesn’t require any special equipment. It can be as simple as having your camera and favorite lens with you. That makes it easy and fun should you want a relatively casual outing or don’t want to be encumbered.
With the addition of a few extras, however, you can cope with more demanding situations and conditions, or simply take different photos. You may benefit from using a tripod, for example, or a remote shutter release. Both provide hands-off stability for your camera.
Regardless of what extra gear you may invest in, you need to configure your camera to shoot the shots you want.