Notes on Water: The Medium of Life

Hydrosphere

• The hydrosphere is the water environment on Earth, comprising water vapor, liquid water, and ice.
• It includes oceans, lakes, rivers, marshes, clouds, snow, and glaciers.
• The hydrosphere is composed of 97.5% saltwater and 2.5% freshwater.

Saltwater

• Saltwater contains salt and is found in oceans and seas.
• It supports marine life and contains mineral resources.

Freshwater

• Freshwater contains small amounts of salt and can be found in rain, snow, and permafrost.
• It is stored in rivers, streams, ponds, lakes, marshes, glaciers, and polar caps.
• Only 1% of freshwater is potable.

Properties of Water

• Density: Water is densest at 3.98°C and less dense when frozen, allowing ice to float and insulate underlying water.
• Transition Temperatures: Water maintains a liquid state at room temperature, facilitating substance transfer in cells.
• Heat Capacity: Water has a high heat capacity, requiring more energy to increase its temperature, which helps regulate temperatures in the environment and within organisms.

Origin of Water

• The prevailing hypothesis suggests that water came from comets colliding with Earth.
• Other studies propose water was present from Earth's formation, trapped in magma and released during degassing.

Uses of Water

• Agriculture: About 70% of global freshwater is used for irrigation.
• Industry: About 20% of water is used globally for manufacturing processes.
• Domestic: About 10% of freshwater is used for drinking, washing, and bathing.