Coat her/him in vaseline,...but make it a thin coat ;-)

Use a polarizer, turned so the reflections on the water are maximum.

       I have to assume you're intending for the surface of the water to be
black, and not the water dripping from your model (which would be next to
impossible, I think). Since the water surface essentially acts like a
moving mirror, the goal is to have it reflect something dark. So this means
a dark background which should wrap to the sides to some extent, since the
reflecting ripples are three-dimensional and can produce some scatter. Dark
ceiling/sky as well. The model should be relatively front-lit, and the
lower the lighting angle the better - best if you can get the lights close
to even with the water's surface so there's little opportunity to bounce
your lighting back to you. Keeping the camera closer to the water level
should be a significant improvement as well.

       For a really black pool, the water should be motionless, which means
getting the model in position and holding perfectly still for a minute or
five - fun! If you're after some small definition from the water, enough to
know that it's water in other words, you'll need *some* reflections to
define the shape of the ripples, and this will probbaly mean playing with
lighting or reflector angles for a bit.

       The other tricky part is if you want the water on the model to show,
drips or streams or the like. Because water shows really well when it's
sidelit to backlit, and the direct lighting mentioned above to keep the
surface dark will show virtually no water on the model. So now you're
talking about sidelights that are blocked off ('barn-doors') to avoid
illuminating the surface while still brightly illuminating the model. Lots
of fun! Remember that water drops act as fisheye lenses, and while they
reflect, they also show what's behind them. So to get definition from a
water droplet, you really need something in the background that has high
contrast. Which can't reflect from the surface...

       Lots to play with! But done well, it should be a neat effect. Promise
to show us the results ;-)

    - Al.