Capture, management, use, disposal, reuse of water

The Human Water Cycle

Capture of Water

Water is first captured from natural sources like rivers, lakes, and rain. Humans use:

• 🌧️ Rainwater harvesting – collecting rain in barrels or underground tanks.
• 🏞️ Reservoirs & dams – storing water for later use.
• 🚰 Groundwater extraction – pumping water from aquifers.

Example: A rooftop in a city can collect enough rainwater to fill a 200 L barrel in just a few days during a storm.

Management of Water

Once captured, water must be managed to keep it safe and useful.

1. 💧 Distribution networks – pipes that deliver water to homes and businesses.
2. 🧪 Water treatment plants – remove impurities using filtration, chlorination, and UV light.
3. 📊 Monitoring – regular testing of pH, turbidity, and bacterial levels.

Mathematical check: Flow rate $Q$ is calculated as $$Q = \frac{V}{t}$$ where $V$ is volume in litres and $t$ is time in hours.

Use of Water

Water is used in three main sectors:

• 🏠 Domestic – drinking, cooking, washing, and bathing. A typical shower uses about 20 L per minute.
• 🌾 Agriculture – irrigation. The UK uses ~70% of its water for farming.
• 🏭 Industry – manufacturing, cooling, and processing. Industries often use >10,000 L per day.

Analogy: Think of water as the “fuel” that powers every activity on Earth.

Disposal of Water

After use, water becomes wastewater and must be treated before returning to the environment.

• 🚽 Sewage – domestic wastewater.
• 🏭 Industrial effluent – contains chemicals and heavy metals.
• 🌱 Greywater – from sinks and showers, less polluted than blackwater.

Wastewater treatment stages: Primary (sedimentation), Secondary (biological treatment), and Tertiary (advanced filtration). The goal is to reduce contaminants to < 1 mg/L of total suspended solids.

Reuse of Water

Reusing water reduces demand on fresh sources.

1. 💧 Greywater recycling – used for toilet flushing or garden irrigation.
2. 🌊 Recycled water – treated to a high standard for irrigation or industrial use.
3. 🧂 Desalination – turning seawater into freshwater using reverse osmosis.

Example: In Singapore, 70% of water used for irrigation comes from recycled sources.