Global water resources: patterns, human water cycle, trends in consumption

🌍 Global Water Resources: Patterns

Water covers about 71 % of Earth’s surface, but only 2.5 % is fresh. Think of Earth as a giant pie: most slices are salty ocean, only a few are fresh‑water “toppings.”

💧 Human Water Cycle

The human water cycle is like a giant water‑wheel: water moves through the atmosphere, land, and oceans, and we tap into it for daily life.

Key Processes

• Evaporation – water turns to vapor from oceans, lakes, and soil. Think of a kettle boiling.
• Transpiration – plants release water vapor. Imagine a forest “breathing.”
• Condensation – vapor cools to form clouds. Picture a cloud as a giant water‑bubble.
• Precipitation – rain, snow, hail fall back to Earth. It’s the water wheel’s “down‑turn.”
• Infiltration & Run‑off – water enters soil or flows over land to rivers and oceans.

Illustration (Text‑Based)

🌞 Sun → 💧 Evaporation → ☁️ Condensation → 🌧️ Precipitation → 🌱 Infiltration → 🌊 Run‑off → 🌊 Oceans → (back to Sun)

📈 Trends in Water Consumption

Water use is growing faster than the global population. The main drivers are:

1. Population growth – more mouths to quench.
2. Urbanisation – cities need more water for households, industry, and transport.
3. Industrialisation – factories consume large volumes for cooling, processing, and cleaning.
4. Climate change – altered rainfall patterns mean more water is needed for irrigation.

Globally, the average per‑capita water use has risen from ~200 L day⁻¹ in the 1970s to over 300 L day⁻¹ today. In many developing regions, consumption is still <100 L day⁻¹, showing huge inequalities.

Analogy: The Water Bank

Imagine the planet’s fresh water as a huge bank account. Every day, we withdraw for drinking, cooking, and industry, but we also deposit through rain and recycling. If withdrawals outpace deposits, the account runs low – that’s water scarcity.