Water Ballooning by Nikebelly80 (Archive Link)
Nice belly-inflation short-story by nikebelly80 on DeviantArt. It follows Hannah and her friend, Emily, during an extremely hot summer. To cool down a bit, they decide to have some fun with the sprinkler and water hose, but due to the pressure, a little accident happens and Hannah finds the hose stuck inside her anus. Quickly starting to enjoy the sensation, she wants to keep it in, especially after Emily inflates her a bit with the cold water.