Ice & water

Our bodies and the Earth are mainly made of water. Water moist the air then rain. Every creatures need more/less water to live. When you cold a glass of water, water change into ice. Ice(solid water) floats in water because of the lower density than water(liquid water). But in general, a solid are heavier than the liquid, and solid also sink in liquid. This strange feature gives important merits for living body. Even in winter, lake don't fully frosed but surfacely. So, many fishes can live under the ice. And as you know, water transport many vital from here to anywhere, and moslty same in our body. KEEPING WATER CLEAN IS GOOD FOR US AND THE ENVIRONMENT. What can we do for first to keep it?