Science of Water : Concepts and Applications

26 The Science of Water: Concepts and Applications
TABLE 2.2
World Water Distribution
Location Percent of Total
Land areas
Freshwater lakes 0.009
Saline lakes and inland seas 0.008
Rivers (average instantaneous volume) 0.0001
Soil moisture 0.005
Groundwater (above depth of 4000 m) 0.61
Ice caps and glaciers 2.14
Total land areas 2.8
Atmosphere (water vapor) 0.001
Oceans 97.3
Total all locations (rounded) 100
Source: From USGS, 2006.
We see from Table 2.2 that the major sources of drinking water are from surface water,
groundwater, and from GUDISW (i.e., springs or shallow wells).
Again, surface water is that water that is open to the atmosphere and results from overland fl ow
(i.e., runoff that has not yet reached a defi nite stream channel). Put a different way, surface water is
the result of surface runoff.
For the most part, however, surface (as used in the context of this text) refers to water fl owing in
streams and rivers, as well as water stored in natural or artifi cial lakes, man-made impoundments
such as lakes made by damming a stream or river, springs that are affected by a change in level or
quantity, shallow wells that are affected by precipitation, wells drilled next to or in a stream or river,
rain catchments, and muskeg and tundra ponds.
Specifi c sources of surface water include:
1. Rivers
2. Streams
3. Lakes
4. Impoundments (man-made lakes made by damming a river or stream)
5. Very shallow wells that receive input via precipitation
6. Springs affected by precipitation (fl ow or quantity directly dependent upon precipitation)
7. Rain catchments (drainage basins)
8. Tundra ponds or muskegs (peat bogs)
Surface water has advantages as a source of potable water. Surface-water sources are usually
easy to locate, unlike groundwater. Finding surface water does not take a geologist or hydrologist
and normally it is not tainted with minerals precipitated from the Earth’s strata.
Ease of discovery aside, surface water also presents some disadvantages: surface-water sources
are easily contaminated (polluted) with microorganisms that can cause waterborne diseases (anyone
who has suffered from “hiker’s disease” or “hiker’s diarrhea” can attest to this), and from
chemicals that enter from surrounding runoff and upstream discharges. Water rights can also present
problems.
As mentioned, most surface water is the result of surface runoff. The amount and fl ow rate of
this surface water is highly variable, for two main reasons: (1) human interferences (infl uences)