Hardness of Rainwater
Country: South Africa
Date: Summer 2009
Is rain water considered as hard water or soft water? Can
anyone drink the rain water if its not an acid rain?
Rainwater is soft water. Water is made "hard" by dissolved calcium or magnesium
ions, neither of which are present in rain water (at least, not until it runs over
calcium- - or magnesium- containing compounds on the Earth's surface).
Richard E. Barrans Jr., Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming
The Ask-A-Scientist archives includes information
on drinking rain water - usually it is safe to
Even rainwater in pristine areas not affected by
air pollution is slightly acidic. That does not mean
that you cannot drink it.
Rainwater is usually "soft". The definition of
"hard" water is water that contains a large amount
of minerals, particularly calcium, magnesium, and iron.
Minerals get into ground water as it passes through the
soil and the bedrock or "hardpan" gravel below the soil.
Most wells contain "hard" water. Most lakes have
fairly soft water unless they are fed primarily by springs
from the ground.
David R. Cook
Climate Research Section
Environmental Science Division
Argonne National Laboratory
I would not want to make a general statement, but rain is the product of the
condensation of water vapor into liquid water. So it "should be" relatively
pure. But to say that anyone can drink rain water would be overstepping the
bounds of possibilities.
Rain water is soft water.
Other people may have other ideas, but I believe you can drink any rain
Acid rain just does not have enough acid or other pollutants in it to hurt
But I would not drink any water out of any streams or rivers.
A common way of purifying water is to boil it to steam then condense the
steam back to liquid in a separate vessel.
That process is called distilling and it leaves most of the impurities that
were in the water behind.
It is a common way of converting salty sea water to fresh water.
Rain is just earth surface water that has evaporated (turned to vapor) into
the air, then recondensed as water in the clouds in rain drops. When the
rain drops get heavy enough to resist the windy updrafts in the clouds, it
falls to earth's surface in the form of rain, or sleet, or hail, or snow if
it is cold enough.
So rain forms by the same process as the distilling process and is pure
enough to drink.
Hard water has dissolved minerals in it that are left behind in the pot
after you convert the water to steam.
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Update: June 2012