I've seen people use a mixture of piping gel and coloring to make water on cakes. Anyone ever use this technique before. How do you do it properly? Plus, would it make the cake taste disgusting or would you have people scrape it off before eating?

I mix the color up before putting it on the cake. No it does not make it taste gross. Its like a sugar icing.

I also mix the color in before I place it. Don't mix it too much or too fast or it'll change the consistency of the piping gel and you lose some of the clearness. I just put it on top of white butter cream so those who get a piece with the water will also have butter cream.