Pretty sure this is it:
Thanks that was really bugging me.
If anyone could help me find a hentai, essentially its in a hot spring, and some girl pisses off another girl which for some reason can control water, so she uses her power to send water into the girl's butt basically giving her an enema. Her belly inflates and after wards she tries to leaves with her bloated belly but she loses control and sprays water all over the floor. I remember it being in black and white and having a slightly cutesy art style.