Environmental Engineering Reference
In-Depth Information
Not everyone, though, is as water wise. We talk more about
water rights in Chapter 5.
WATER BASICS: A PRIMER
To understand why and how global water issues affect all of us, we
fi rst must understand how and where we get our water. Hydrology
involves much more than calculating precipitation, evaporation, or
how much water is underground or on the Earth's surface in our
lakes and rivers.
The Water/Hydrologic Cycle
The movement of water, and the various forms it takes, is known
as the
water cycle
or
hydrologic cycle
. It's a closed cycle—water doesn't
escape into space. It has no beginning and no end; it's perpetual.
(Figure 2.1 illustrates this constant state of motion.) Some bit of that
water you just had in some form most likely came from distant places
and distant climates at some time in the distant past. Earth, then,
could be considered the ultimate recycler when it comes to water.
The amount of water on Earth doesn't change. It's the same
today as it was yesterday, the day before, decades before, and mil-
lions of years ago. What does change, though, is the movement of
that water; the form it takes (liquid, ice, or vapor); the degree of its
purity, and its accessibility.
Let's look more closely.
Water supplies.
The Earth's supply of freshwater basically comes
from two sources: surface water and underground water.
Surface water.
Including rain, snow, ice, or variations of the
three, this aboveground water fi lls our lakes, rivers, and
streams.
Underground water
. Water found beneath the ground is known
as an
aquifer
, and very often is pumped out of the ground for
various uses. The top level of the aquifer is the
water table
.
An aquifer is like a constantly moving, giant storage basin—up
to tens of thousands of square miles in area—of loose rocks, sand,
