Short answers, pulled from the story.
Water expands when it freezes because hydrogen bonds form a hexagonal lattice that creates open spaces, making ice about nine percent less dense than its liquid form. This density anomaly allows ice to float and keeps aquatic life alive beneath winter's crust. The bent molecular structure of H2O is the root cause of this rare property.
Water supports life in living cells through its polarity, which creates a dipole moment that drives the hydrophobic effect and forces nonpolar molecules to cluster together. This polarity dictates the structure of proteins and the pairing of DNA bases, enabling the folding of proteins and the replication of genetic code. Water acts as both a solvent and a reactant in hydrolysis and condensation reactions essential for metabolism.
The hydrologic cycle is the continuous movement of water through the atmosphere, land, and oceans that has sculpted the Earth's surface over billions of years. It begins with evaporation from oceans and transpiration from plants, sending water vapor into the atmosphere where it condenses to form clouds and falls as precipitation. This cycle drives ocean currents like the Gulf Stream that moderate global climate and transport warm water from the equator to the poles.
The earliest civilizations developed along the banks of major rivers, with Mesopotamia rising between the Tigris and Euphrates rivers and ancient Egypt depending on the annual flooding of the Nile. The Indus Valley civilization flourished along the Indus River, and Rome was founded on the Tiber. These waterways provided drinking water, transportation, and trade routes that enabled human civilization to flourish.
Water has been detected in the atmospheres of stars, the rings of planets, and the subsurface oceans of moons throughout the universe. NASA's Moon Mineralogy Mapper confirmed water in the Moon's polar craters and volcanic rocks in 2009, and liquid water may exist beneath the icy crusts of Jupiter's moon Europa and Saturn's moon Enceladus. Water vapor has also been found in the atmosphere of the exoplanet HD 189733 b, located 63 light-years from Earth.
The United Nations estimates that 2.2 billion people do not have access to safely managed drinking water and 4.2 billion lack access to safely managed sanitation. Water scarcity is a growing crisis with demand expected to exceed supply by 50 percent in some developing regions by 2030. The World Health Organization estimates that five million deaths per year are caused by water-related diseases.