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30 Chapter 2 Water Sources: Surface Water
Distribution of Earth’s Water
Freshwater 3% Other 0.9% Rivers 2%
Surface
Ground- water Swamps 11%
water 0.3%
30.1%
Saline
(oceans) Icecaps Lakes
97% and 87%
glaciers
68.7%
Figure 2.1 Distribution of Earth’s
Earth’s water Freshwater Fresh surface Water
water (liquid) (Courtesy of USGS)

Table 2.1 Estimated Water Distribution on Earth
3
2
Surface Area (mi ) Volume (mi ) % of Total
Salt Water
The oceans 139,500,000 317,000,000 97.2%
Inland seas and saline lakes 270,000 25,000 0.008

Freshwater
Freshwater lakes 330,000 30,000 0.009
All rivers (average level) — 300 0.0001

Antarctic ice cap 6,000,000 6,300,000 1.9
Arctic ice cap and glaciers 900,000 680,000 0.21
Water in the atmosphere 197,000,000 3,100 0.001
Groundwater within half a mile
from surface — 1,000,000 0.31
Deep-lying groundwater — 1,000,000 0.31
Total (rounded) — 326,000,000 100.00

2
3
6
2
3
2
Conversion factors: 1 mile 1.609 km; 1 mile 640 acre 2.59 km 2.59 10 m ; 1 mile 4.1673 km .
Source: Courtesy of U.S. Geological Survey.
ocean) as groundwater discharge, and some groundwater finds openings in the land surface
and emerges as freshwater springs. Over time, though, all of this water keeps moving; some
reenters the oceans, where the water cycle “ends”—or, where it “begins.”
2.1 SOURCES OF SURFACE WATER
In the United States by far the largest volumes of municipal water are collected from sur-
face sources. Possible yields vary directly with the size of the catchment area, or water-
shed, and with the difference between the amount of water falling on it and the amount lost