Shooting waterfall is always interesting. All you need is the right gear. First, choose any DSLR, be it super expansive or cheap type, as long the shutter speed can be set manually, it will work just fine.
Second, get a sturdy tripod as you may want to avoid blurry image due to long shutter speed mode. For those who love perfection, get a remote release button or release cable to avoid any camera shake while pressing the shutter button. For me, the auto-timer function is sufficient enough.
Once you set your shutter speed to a long speed, adjust the ISO for the correct exposure and shoot in auto-timer, you will get a nice silky flowing water. It so easy.