In October 1611, Cosimo II De' Medici sponsored a debate in Florence starring Galileo on "Why ice floats on water." 400 years later 25 scientists commemorated the event, revisiting all things to do with water: modern views on Galileo, fresco restoration, cement. Water, its history, in jellyfish; solutions of salts and specific ion effects in biology; of light and magnetic fields on water; dissolved gases. It became clear that the foundations of the theories of physical and colloid chemistry that underpin science, from chemical engineering to molecular and cell biology, even climate science, face serious challenges. As in Galileo's time the science is not settled. And we still can not explain why ice floats on water. A serious revision is called for and is under way.