I am making a variation of the cake attached...couple of questions
1) when tinting my piping gel to get the water effect.,can I just use blue food coloring or do I have to buy wilton's color gels
2) should i layer buttercrea, than piping gel over the buttercream to get the water effect...or can I just apply the tinted piping gel on the cake (it;s a vanilla cake)

thanks

When I did a cake with water on it (seashore-themed retirement cake), I did a base icing in buttercream first, because the piping gel is pretty transparent, and I thought the cake texture would show through. Also, I used a pale blue icing, to add a little more depth to the color.

I don't know about the liquid colorings, but it wouldn't hurt to try tinting a small amount of gel to the shade you want and see if the amount of coloring thins it too much.