Water resources are significantly affected by a range of human activities, including deforestation, industrialization, agricultural development, mining, construction, and transportation. These activities can lead to pollution, depletion, and alteration of natural water systems.
Agricultural development has both positive and negative impacts on water resources. While essential for food production, it is also the largest consumer of freshwater, placing a significant strain on local water supplies.
Agriculture is the primary user of freshwater globally. Water used for irrigation takes a long time to return to the water cycle, reducing availability for other uses.
The use of pesticides, herbicides, and fertilizers is a major source of water pollution:
BOD is the amount of dissolved oxygen required by aerobic microorganisms to decompose organic matter in a water sample at a given temperature. A high BOD value indicates heavy organic pollution — bacteria consume large amounts of breaking down waste, depleting oxygen available for aquatic life.
Poor land management and excessive tilling cause soil erosion. Eroded soil washes into rivers and lakes, filling their beds and making them shallower, reducing their capacity to hold water.
The extensive use of tube wells for irrigation leads to the over-extraction of groundwater. This results in the depletion of aquifers (underground layers of water-bearing rock). Replenishment of aquifers depends on rainfall, which is often insufficient to recover the amount of water withdrawn.
Industrial activities introduce a wide array of pollutants into water bodies and consume large volumes of water, impacting local supplies and ecosystems.
Industrial units release pollutants such as:
These pollutants render water unfit for drinking and recreational use, and are toxic to aquatic species.
Industries use vast quantities of water for processes like condensation, cooling, and as a solvent. The use of water as a coolant, in particular, can be enormous, putting a strain on local water supplies.
Industries often release heated water into nearby rivers or streams. This increases the water temperature, which reduces the solubility of dissolved oxygen () according to Henry's Law. Low oxygen levels make the water uninhabitable for certain species, such as trout, which require cold, oxygen-rich water to survive.
Large-scale projects like dams and canals can alter the natural flow of rivers, disrupting aquatic ecosystems over large regions. Extractive industries such as mining can dislodge groundwater sources and destroy local streams.
To counter these impacts: