Environmental Engineering Reference
In-Depth Information
7
Physical Dr
inking Water Parameters
Water is H
2
O, hydrogen two parts, oxygen one, but there is also a third
thing, that makes it water and nobody knows what that is.
—D. H. Lawrence (1885-1930)
Before enlightenment, Chop wood
Carry water.
After enlightenment, Chop wood
Carry water.
—Zen saying
Introduction
Sometimes obvious questions are the most difficult to answer, especially
if they are asked out of the clear blue sky (so to speak). What would your
answer be if you were asked to describe at least one physical property of
water? The most likely response would be that “water is wet.” In saying so,
we have provided not only the simplest response but also the one that is
most obvious to us. Water is indeed wet. Water's wetness is perhaps its most
obvious physical characteristic.
But, let's assume that the query does not end there and that the next ques-
tion posed to us is “What makes water wet?” With this question, we leave the
realm of general knowledge; unless we are practitioners of water science, this
question may be beyond our ability to answer.
Let's look at the answer anyway. Why? Because we are water practitioners
… and we should have some idea of why water is “wet.” According to David
Clary (1997), a chemist at University College London, water does not start
to behave like a liquid until at least six molecules form a cluster. He found
that groups of five water molecules or fewer have planar structures, forming
films one molecule thick; however, when a sixth molecule is added, the clus-
ter switches to a three-dimensional cage-like structure that suddenly has the
properties of water—it becomes wet.
This information is all well and good, but what else do we need to know?
Other physical characteristics of water we are interested in are probably
somewhat more germane to the discussion at hand—namely, categories and
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