freshwater

Fresh water or freshwater is any naturally occurring liquid or frozen

water

containing low

concentration

s of dissolved salts and other total dissolved solids. Although the term specifically excludes

seawater

and brackish water, it does include non- salty mineral-rich waters such as chalybeate springs. Fresh water may encompass

frozen

and meltwater in

ice sheet

s, ice caps,

glacier

s, snowfields and

iceberg

s, natural

precipitation

s such as

rain

fall,

snowfall

,

hail

/

sleet

and

graupel

, and surface runoffs that form inland bodies of water such as

wetland

s,

pond

s,

lake

s,

river

s,

stream

s, as well as

groundwater

contained in

aquifer

s, subterranean rivers and lakes.

Water is critical to the survival of all living

organism

s. Many organisms can thrive on salt water, but the great majority of higher plants and most

insect

s, amphibians,

reptile

s, mammals and

bird

s need fresh water to survive.

Fresh water is not always

potable water

, that is, water safe to drink by

human

s. Much of the

earth

's fresh water (on the surface and groundwater) is to a substantial degree unsuitable for human consumption without some treatment. Fresh water can easily become

polluted by human activities

or due to naturally occurring processes, such as erosion.

Fresh water is a renewable and variable, but finite natural resource. Fresh water can only be replenished through the process of the

water cycle

, in which water from seas, lakes, forests, land, rivers and

reservoirs

evaporates, forms

cloud

s, and returns inland as precipitation. Locally, however, if more fresh water is consumed through human activities than is naturally restored, this may result in reduced fresh water availability (or

water scarcity

) from surface and underground sources and can cause serious damage to surrounding and associated environments.

Water pollution

and subsequent

eutrophication

also reduces the availability of fresh water.

Definitions

Numerical definition

Fresh water can be defined as water with less than 1000 parts per million (ppm) of dissolved salts.

Other sources give higher upper salinity limits for fresh water, e.g. 1000 ppm or 3000 ppm.

Systems

Fresh water habitats are classified as either lentic systems, which are the stillwaters including

pond

s, lakes,

swamp

s and

mire

s; lotic which are running-water systems; or

groundwater

s which flow in rocks and

aquifer

s. There is, in addition, a zone which bridges between groundwater and lotic systems, which is the hyporheic zone, which underlies many larger rivers and can contain substantially more water than is seen in the open channel. It may also be in direct contact with the underlying underground water.

Sources

The original source of almost all fresh water is precipitation from the

atmosphere

, in the form of

mist

,

rain

and

snow

. Fresh water falling as mist, rain or snow contains materials dissolved from the

atmosphere

and material from the sea and land over which the rain bearing clouds have traveled. The precipitation leads eventually to the formation of

water bodies

that humans can use as sources of freshwater:

pond

s,

lake

s,

rain

fall,

river

s,

stream

s, and

groundwater

contained in underground

aquifer

s.

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. This can give rise to elevated concentrations of

sodium

,

chloride

,

magnesium

and

sulfate

as well as many other compounds in smaller concentrations.

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

.

Water distribution

Saline water in

ocean

s,

sea

s and saline

groundwater

make up about 97% of all the water on

Earth

. Only 2.5–2.75% is fresh water, including 1.75–2% frozen in

glacier

s,

ice

and snow, 0.5–0.75% as fresh groundwater and

soil

moisture, and less than 0.01% of it as surface water in

lake

s,

swamp

s and

river

s. Freshwater lakes contain about 87% of this fresh surface water, including 29% in the

African Great Lakes

, 22% in

Lake Baikal

in Russia, 21% in the North American Great Lakes, and 14% in other lakes. Swamps have most of the balance with only a small amount in rivers, most notably the

Amazon River

. The atmosphere contains 0.04% water. In areas with no fresh water on the ground surface, fresh water derived from precipitation may, because of its lower density, overlie saline ground water in lenses or layers. Most of the world's fresh water is frozen in

ice sheet

s. Many areas have very little fresh water, such as

desert

s.

Freshwater ecosystems

Threats and challenges

The increase in the world population and the increase in per capita water use puts increasing strains on the finite resources availability of clean fresh water. The response by freshwater ecosystems to a changing climate can be described in terms of three interrelated components: water quality, water quantity or volume, and water timing. A change in one often leads to shifts in the others as well. However, National Geographic suggests limiting our own water consumption to combat the ongoing water crisis.

Limited resource

Minimum streamflow

An important concern for hydrological ecosystems is securing minimum

streamflow

, especially preserving and restoring instream water allocations. Fresh water is an important natural resource necessary for the survival of all

ecosystem

s. The use of water by humans for activities such as irrigation and industrial applications can have adverse impacts on down-stream ecosystems.

Fresh water withdrawal is the quantity of water removed from available sources for use in any purpose, excluding evaporation losses. Water drawn off is not necessarily entirely consumed and some portion may be returned for further use downstream.

Water pollution

Global goals for conservation

The

Sustainable Development Goals

are a collection of 17 interlinked global goals designed to be a "blueprint to achieve a better and more

sustainable

future for all".United Nations (2017) Resolution adopted by the General Assembly on 6 July 2017, Work of the Statistical Commission pertaining to the 2030 Agenda for Sustainable Development
A/RES/71/313
Targets on freshwater conservation are included in

SDG 6

(Clean water and sanitation) and

SDG 15

(Life on land). 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

." Another target, Target 15.1, is: "By 2020, ensure the conservation, restoration and sustainable use of terrestrial and inland freshwater ecosystems and their services, in particular forests,

wetland

s,

mountain

s and drylands, in line with obligations under international agreements."

Human uses

Uses of water include

agricultural

, industrial,

household

, recreational and

environmental

activities.

Water used for agriculture is called "agricultural water" or farm water.

Animals

Water is a critical issue for the survival of all living organisms. Some can use salt water but many organisms including the great majority of higher plants and most mammals must have access to fresh water to live. Some terrestrial mammals, especially desert

rodent

s, 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.

See also

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References

External links

The World Bank's work and publications on water resources



Fresh Water National Geographic

{{Authority control

Aquatic ecology
Hydrology
Water supply