Environmental Engineering Reference
In-Depth Information
Water storage in
ice and snow
Water storage in the atmosphere
Condensation
Sublimation
Evapotranspiration
Precipitation
Evaporation
Surface runoff
Snowmelt runoff
to streams
Stream flow
Evaporation
Infiltration
Spring
Freshwater
storage
Water storage
in oceans
Ground-water storage
FIGURE 3.5
(See color insert.) The water cycle. (From United States Geological Survey, Summary of the water cycle, http://
ga/water.usgs.gov/edu/watercyclesummary.html, 2010a.)
snow, rivers and streams, lakes, swamps, and groundwater that provides people with the
water needed to live. Figure 3.6 shows the percent distribution of Earth's water, with the left
column indicating 97% of this water is saline and only 3% is freshwater. Moving to the mid-
dle column, we see the 3% of freshwater breaking down into a majority of ice (68.7%) and a
smaller percentage (30.1%) as groundwater. This leaves only 0.3% of Earth's total water on
the surface, and as shown by the right column, a small percentage is held in primarily in
lakes (87%), and the rest in rivers, streams, and swamps.
Table 3.1 presents a more detailed accounting of Earth's water reserves; specifically
where the water resides, the estimated quantities within these reservoirs, and the amounts
of freshwater as a percentage of total water (Shiklomanov 1993; Jones 1997).
The major lessons learned from the characteristics of Earth's water are (1) most of our
water is not potable and the accessible portion of potable water is small and (2) contamina-
tion of a significant amount of our potable water resources can and does create regional
shortages, despite the existence of an adequate supply of freshwater per capita on Earth.
3.2.4 Potable Water Use
The term potable water means water used for any human purpose (Fuhrer et al. 1999) and
includes uses other than drinking water. From a water quality standpoint, potable water
contains less than 10,000 μg/L of total dissolved solids. In the United States, potable water
use includes: (modified from Fuhrer et al. 1999)
Search WWH ::




Custom Search