why is HYDROSPHERE referred to as clear liquid gold?

Hydrosphere is the liquid content of earth, this includes lakes, oceans, rivers and ponds etc. About 70% of earth is covered by water. They probably call the hydrosphere as clear as liquid gold because the water on earth was originally very clean until us humans polluted it? that sounds cool =P

You'd best ask the poet who came up with the analogy. Most people think it refers to the Earth's supply of water. Perhaps the poet wished to metaphorically stress its value.