IMPORTANT NOTE REGARDING THE USE OF WATER CAKES: 
Water cakes should NEVER be fired vertically.  Water cakes are designed to be fired into a large body of water such as a lake or large river.  Water cakes should be angled approximately 30 to 45 degrees and pointed away from the setup area and spectators toward a large area of open water. 
Water cake inserts are specifically manufactured with time delay fuses that are longer than a standard cake insert.  Once launched the cake inserts will travel a long distance before landing in the water where they will perform their effect directly on the surface of the water.