Some people choose to not have squirt/water guns in their home so if that is you, you could always alter this with spray bottles, a hose, ketchup bottle etc.
I love the idea of setting up a little target practice for summer water cowboy fun! Planet of the Apels made one from wood, golf tees, and ping pong balls.
Mexico Migration used soda bottles!
Apple Falls set up targets using tissue paper
and Busy Kids = Happy Mom made an indoor target with cups and minifigs!