Environmental Science / Unit 6: Water Resources and Pollution
6.2 Freshwater Use and Scarcity
Notes
People use freshwater for agriculture, industry, and households.
- Globally, agriculture uses about 70% of freshwater withdrawals; industry about 20%; households about 10%.
- Withdrawal is water taken from a source. Consumptive use is water not returned to the source (for example, evaporated from irrigated crops).
- Overpumping an aquifer lowers the water table, can cause land subsidence (sinking ground), and near coasts allows saltwater intrusion. The Ogallala Aquifer under the US Great Plains is being depleted faster than it recharges.
- Dams provide water storage, hydroelectric power, and flood control but flood habitat, trap sediment, and block fish migration.
- Water-saving options: drip irrigation, fixing leaks, low-flow fixtures, reuse of treated wastewater, and desalination (energy intensive).
- Example: drip irrigation sends water directly to roots and wastes less than spraying a field.
Practice
Which sector uses the most freshwater worldwide?
Irrigation accounts for about 70% of withdrawals.
What is a harmful effect of heavy pumping of groundwater near the coast?
Lowering freshwater pressure lets seawater move into the aquifer.
Which irrigation method is the most water efficient?
Drip irrigation delivers water to the roots and limits evaporation.
Ready for more? Take the Unit 6 test.