Water security: availability, demand, quality and sustainable use
What this domain tests
Water security is broader than "enough rain". This domain tests the pillars - availability, access, quality, affordability and resilience to drought and flood - and the ability to judge whether a supply is adequate, stressed or scarce.
Core rules and concepts
- How little is usable: about 97.5% of Earth's water is saline; most freshwater is locked in glaciers and ice caps, leaving well under 1% of total water accessible in rivers, lakes and shallow aquifers.
- Falkenmark thresholds (renewable freshwater per person per year): above 1,700 m³ adequate; 1,000–1,700 m³ water stress; below 1,000 m³ water scarcity; below 500 m³ absolute scarcity. India has fallen from roughly 5,000 m³ in 1951 to about 1,500 m³ today.
- Demand: irrigation takes about 78–80% of India's water, then domestic use, then industry. Demand rises with population, urbanisation and water-hungry crops such as sugarcane in Maharashtra's dry zones.
- Quality: BIS 10500 specifies pH 6.5–8.5; total dissolved solids 500 mg/L acceptable and 2,000 mg/L permissible; fluoride 1.0 mg/L (1.5 permissible); arsenic 0.01 mg/L; nitrate 45 mg/L. Excess fluoride causes fluorosis, documented in parts of Marathwada and Vidarbha.
- Sustainable use: demand management - drip and sprinkler irrigation, crop choice, leakage repair, tariff reform - before new supply.
Worked example
A district has 1,200 million m³ (MCM) of usable annual supply and 1.5 million people. Per capita availability = 1,200,000,000 ÷ 1,500,000 = 800 m³/year. That is below the 1,000 m³ scarcity line, so the district is water-scarce even before industrial demand is counted - and a plan built on "average rainfall" would hide the deficit.
Traps that cost marks
Confusing water stress with water scarcity. Quoting 2,000 mg/L TDS as the acceptable rather than the permissible limit. Treating water security as a rural issue only - urban supply hours and leakage count equally.