Super Soaker Central

Im not sure are they very tpugh to build? Im just after a gun with a good range say 35-40 feet that doesnt look like a gun and will take people by surprise

Well, we can make better suggestions with more specifics. Do you need to be able to pump the blaster right after shooting? How much do you want to soak your targets? Do you need a design by a certain time? What will it be used for (i.e. assassins, water war games, pranks, etc)? In particular, the last question is very helpful in determining what kind of design would be most useful.