The quality of freshwater depends on the kinds and amounts of substances dissolved in or carried by water (including pollutants, such as toxins and gases), and on how those substances impact the desired use of the water, from drinking, household purposes, agriculture, recreation, or industrial processes. The availability of useable freshwater depends on the size of the reservoir (water source), the rate of replenishment of the reservoir, and on water quality.
A variety of human and environmental changes can cause changes to water quality and availability, including:
- Decreases in precipitation, which can change the amount of water available seasonally and over longer periods of time (years to decades). Global warming contributes to the severity and frequency of droughts as warming changes atmospheric circulation patterns and the water cycle.
- Decreases in snow and ice cover due to global warming. In many regions, snow and ice melt provides freshwater for human use and for ecosystems. With decreased snow and ice to melt, there is less freshwater available and reserves are more easily depleted.
- Increases in freshwater use, especially to meet the needs of population growth, agriculture and industrial process can reduce the amount of water available for humans and other organisms.
- Pollutants and waste from industry and agriculture can decrease the quality of freshwater, which can affect the health of humans and ecosystems.
- Deforestation and invasive plant species can alter stream habitats, increasing erosion and sedimentation thereby decreasing water quality.
Can you think of additional cause and effect relationships between food availability and nutrition and other parts of the Earth system?