I still have not encountered a situation where I would need a waterfall, for now I am just curious, but would really apreciate any answers.
Debbie Brown colours piping gel blue and swirls this around with a spoon to create water. I have a rather ancient book by Jane Asher who created something she called "toffee glass" for a bathing pool, heres the recipe:
Heat 250g granulated sugar in 150ml water until sugar dissolves. Bring to the boilmtill you reach the "soft crack" stage before mixture starts to colour. Remove and use immediately. I think by "soft crack" stage she menas when droplets set in cold water or if you could use a sugar thermometer. She made a blue coloured icing with water and seived icing sugar which she poured into her pool and added the toffee glass after the water icing had set. This gave a sheen to the water and it crystallised a little making the water look turbulent. Hope this helps, Im sure there are many ways of getting the effect you want
Sometime soft crack stage is approximately 98 deg. above your stove's boiling point. Works for me.