The photo below is an image of a cheap plastic water bottle, you can see the white-colored cap on top. However, I am not sure how the lighting was done. For sure no expensive strobing has been used. I wonder if the coloring has been done only in post-processing. Please note that the droplets appear in at least three different colors. Any thoughts?
For colored water drops, you put colored filters on the flash. Technically, you cannot change the color of the water, you change the color of whatever the water is reflecting. On that one, the white cap is blue too.
You can put different filters on a couple flashes to mix colors. For example, blue and red was used on two flashes for this one: http://www.scantips.com/drops/shako/