Not much.
Ice is only water, when the molecules are submitted to low temeperatures and have formed a crystalline arrangement of low density. In ice, the molecules arange themselves in hexagons with hydrogen bonds binfing each molecule.
When ice melts it turnes into water and the molecules leave the crystalline shape and come back to their normal density. In water, not all molecules are binded forming short and irregular lines.
→ In the image below, you can see the arrangement of ice and water.
Hope it helped,
BioTeacher101
