User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-4902593-20130225075602/@comment-2079715-20130303134051

Not water to ice, but ice to water. I believe he did it in the Son of Neptune, when he refilled bottles of water for him, Frank and Hazel, after gryphon attacks. Ofc, it's possible that I misunderstood the paragraph.