Water is an inorganic, transparent, tasteless, odourless, and nearly colourless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms. It is vital for all known forms of life, even though it provides no calories or organic nutrients. Water forms the seas, lakes, rivers, and rain and is the basis of the fluids of living organisms. The significant sources of freshwater are the rivers, ponds, springs and glaciers. The movements that occur in oceans can be broadly categorised as waves, tides and currents. Ice, snow, and frost are examples of water in the solid-state.