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A material or molding substance that can dissolve in water not to fast but decently quick an floats in water

i am trying to build a prototype dnt want to share to much about it hoping to sell it an patent it n e ways i am trying to figure out a material where i can mold it like clay an make like  obkects out of it an at the same time if i where to pour water on it the item would dissolve at the same time float so say i put a snow ball in the tub an it was packed well an it floats an i want to shoot it with a water gun a good water gun an made it dissolve thats what im trying to get at basically with the material i need it floatable an non harmful an dissolves an can be molded please help