My guess is that professionals would just shoot the 'fall' without a raindrop, probably using a crane, and add the drop in digitally later.
This could mean learning a 3D modeling program, though.
You will need a camera like a Red or even a Varicam to shoot that. 120fps or more is needed to catch the real thing. Or 60fps if you have Twixtor.
But the only thing that needs to be real is the final 2ft of the fall and the imapct on the flower. You can get a pretty good rain drop by generating it in something like Cinema 4D and following that drop with a virtual cam.
But if you dont have C4D then do this.
Get a latter and a sturdy mount for the cam to be upside down and well supported. (10 ways to do that) We used a pain of glass on 2x4's to hold the camera above the ground to film a bottle dropping and breaking in semi slow mo.
For the rain drop you will have to use a glass pain over a camera pointed directly at the sky. Then climb a latter and drop the liquid on to that pain as close to middle as possible. (20 takes easy)
Then you can show the drop from 3 angles; over head, the ground looking up and impact from whatever angle does best.
Try water but i am sure you will need to mix KY Jelly with water to make it thicker and so that it will hold its form during the fall.
Try to find something that will create the largest possible rain drop. The liquid having a thicker viscosity will help. Experiment with it.
Here's a diagram.
From the original question it sounds like he/she is after a single follow shot (cloud to flower), in which case it'll always be done in CG apart from the impact at the end. Not only can you do photo-real water in CG with relative ease, it's a whole heap faster and less expensive than building a drop rig. If you wanted real footage of a falling drop from the drop's point of view, you'd need to build a laminar flow tube so the drop can be held stationary in a rising column of air. It's possible but hideously difficult to get right.
For the real footage of a drop hitting something I second the suggestion of using Twixtor - the fluid motion involved lends itself very well to Twixtor's morph algorithm. The question is all about resolution; many consumer camcorders can shoot 120fps or higher but at stupidly-low res. If you want 1080p at a fast enough frame rate for Twixtor to work with then you will need a pro camera. Some of the latest sensors can run fast enough to avoid the need for post, e.g. the recently-announced NEX-FS700 will shoot 300fps at 1080p, and up to 960fps at reduced res, but you'll need vast amounts of light (10kW of tungsten would get you started at 300fps). FS700 example clip here.
There are some decent fluid dynamics plugins for MAX and Maya (e.g. Glu3D) which could do a passable job of rendering a water splash entirely in CG, in fact the hard part would be modeling the flower's reaction to the force rather than the water itself.
Cheers Preditor Corbett, that looks great to me. I have access to pretty much everything I need minus the glass but I'm sure I can pick that up easy enough!! I wasn't looking to do it in one shot, in actual fact I need about 3 different angles in it so this will be ideal. Thanks again!