Im wanting to stick fondant crayons in random directions all over the sides of the cake (sort of like the picture below but in different direvtions). Am I going to have a problem getting these things to stick if just using water? Im afraid the weight of the crayons will make it not stick causing a runny colored mess all over cake as they sag down or fall off!

You will need to go very light on the water   You probably would be better off to use melted chocolate 

I agree with melted chocolate for something with that kind of weight.

I use melted chocolate all the time because it is what I always have on hand.  You could also use royal icing, but I definitely would not use water or even edible glue made with water and tylose.

Sandra has done more of this type of work than I have so heed her advice.

Lynne, that is because I can't pipe!  It is called desperation!