Camera: Canon EOS 400D / Rebel XTi
Lens: Canon EF 100/2.8 Macro USM lens
Exposure: 0.005 sec (1/200)
Aperture: f/0
Focal Length: 100 mm
ISO Speed: 100

First lets start with the home studio set up

For starters, a water drop needs to fall into something that is clear enough for you to be able to focus directly through. As you can see by my setup below, a fish tank was perfect for this. Next, I knew for me to have the best chance of capturing the drop, it had to roughly fall into the same area with each splash. Hence, I placed a bag with a small pin hole over the top of the tank. If your following along with this home studio setup, it's also important that you have good lighting and a nice cardboard background placed behind the tank for color.

Where exactly do you need to focus?

When photographing water, it's best to set your digital SLR camera to either shutter priority or manual mode (if using an extention tube). You also need to turn off your lens AF (automatic focus). Instead, prefocus through the glass and onto the tip of a pencil, held approximately 1cm above the water in the same area you anticipate the droplet to fall. When you look through the view finder, you should see a red focal point, flashing somewhere around the pencil tip. As this happens, take notice of the position you're standing from the subject. This is how you'll need to be when taking the photographs. Don't turn your camera off or change the lens focal length at this stage, or your settings will be lost. Now you're ready to pierce a small hole in that bag and start taking photographs.

Other useful tips

• Make sure you use a real macro lens for best results.
  
  
• You need to literally need to take hundreds of photographs to get a couple you will like.
  
  
• Practise makes perfect. Macro water photography takes a lot of patience.
  
  
• Try different colored backgrounds. For example, the image below was photographed with a red piece of cardboard placed behind the tank. No photoshop editing has been used other than to resize for display purposes. Hence, the red color is shown exactly how the photo was saved directly from the camera.
  

Info taken from www.slrphotographyguide.com