Fresh water
Fresh water may encompass frozen and meltwater in ice sheets, ice caps, glaciers, snowfields and icebergs, natural precipitations such as rainfall, snowfall, hail/sleet and graupel, and surface runoffs that form inland bodies of water such as wetlands, ponds, lakes, rivers, streams, as well as groundwater contained in aquifers, subterranean rivers and lakes.
Much of the earth's fresh water (on the surface and groundwater) is to a substantial degree unsuitable for human consumption without treatment.
Fresh water can easily become polluted by human activities or due to naturally occurring processes, such as erosion.
As some of those aquifers formed hundreds of thousands or even millions of years ago when local climates were wetter (e.g. from one of the Green Sahara periods) and are not appreciably replenished under current climatic conditions - at least compared to drawdown, these aquifers form essentially non-renewable resources comparable to peat or lignite, which are also continuously formed in the current era but orders of magnitude slower than they are mined.
The original source of almost all fresh water is precipitation from the atmosphere, in the form of mist, rain and snow.
The precipitation leads eventually to the formation of water bodies that humans can use as sources of freshwater: ponds, lakes, rainfall, rivers, streams, and groundwater contained in underground aquifers.
In coastal areas fresh water may contain significant concentrations of salts derived from the sea if windy conditions have lifted drops of seawater into the rain-bearing clouds.
In desert areas, or areas with impoverished or dusty soils, rain-bearing winds can pick up sand and dust and this can be deposited elsewhere in precipitation and causing the freshwater flow to be measurably contaminated both by insoluble solids but also by the soluble components of those soils.
Significant quantities of iron may be transported in this way including the well-documented transfer of iron-rich rainfall falling in Brazil derived from sand-storms in the Sahara in north Africa.
[9] In Africa, it was revealed that groundwater controls are complex and do not correspond directly to a single factor.
The years of most recharge coincided with the most precipitation anomalies, such as during El Niño and La Niña events.
This understanding is particularly crucial in Africa, where water resources are often scarce and climate change poses significant challenges.
[12] Groundwater plays a crucial role as the primary source of water for various purposes including drinking, washing, farming, and manufacturing, and even when not directly used as a drinking water supply it remains vital to protect due to its ability to carry contaminants and pollutants from the land into lakes and rivers, which constitute a significant percentage of other people's freshwater supply.
Some terrestrial mammals, especially desert rodents, appear to survive without drinking, but they do generate water through the metabolism of cereal seeds, and they also have mechanisms to conserve water to the maximum degree.Freshwater ecosystems are a subset of Earth's aquatic ecosystems that include the biological communities inhabiting freshwater waterbodies such as lakes, ponds, rivers, streams, springs, bogs, and wetlands.
Freshwater habitats can be classified by different factors, including temperature, light penetration, nutrients, and vegetation.
[22]: 11 An important concern for hydrological ecosystems is securing minimum streamflow, especially preserving and restoring instream water allocations.
Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater.
For example, Target 6.4 is formulated as "By 2030, substantially increase water-use efficiency across all sectors and ensure sustainable withdrawals and supply of freshwater to address water scarcity and substantially reduce the number of people suffering from water scarcity.
