Ask A Scientist Chemistry Archive

Question:  I want to remove chlorine from tap water so plants I water
with the tap water are not harmed by the chlorine.  Is there a safe, 
cheap, and effective chemical I could use?
 tom hammargren

Answer 1:
You can boil the water for fastest results but a real waste of energy.
You can just leave water on the shelf for a few days or place
in the sun for speedier results.  A test kit from a pool supply store
may help you decide if the Cl has been depleted enough.  This
treatment will allow volatile molecules (like chloroform too) to
dissipate but not larger molecules (eg., PCBs).  Good Luck!
 michael b lomonaco

Answer 2:
Tom,
 
Do yo have any evidence that the chlorine is actually harming the
plants?
 
Ric

Answer 3:
To remove chlorine quickly and easily, go to a fish supply store and 
purchase dechlorinator.  The cheap brands are as good as the expensive 
ones. The cheap brands are very inexpensive.  To answer Ric's question, 
chlorine in tap water is known to cause chloridosis, or yellowing of 
leaves.  Some water treatment facilities are using an aminated chlorine 
that is not as easily removed by allowing the water to sit out.  I strongly 
suggest the use of commercial dechlorinator.
Stacie

Answer 4:
Stacie,
 
  I'm not sure that I buy the assertion that chlorine in tap water
is present in sufficient quantities to cause chloridosis.  Using
the dechlorinator you mention can actually inadvertently remove
other trace mineral salts needed by plants.
 
  Naturally my note above is THEORY; this would be a good opportunity
to experiment by using water from various sources, including the
dechlorinated variety you mention. Such an experiment can include
data on water pH, and iron concentration, which are the two most
common causes of yellowing in plants.  Naturally this experiment
can be made as complex as desired.  One thing you might do for
some info is to get a bottle of a commercial fertilizer and
try to determine the chlorine concentration it would have when
mixed with regular tap water according to its directions.  You
can comment on whether you think the level of chlorine due to
the fertilizer is much affected by any chlorine in the tap water
or not.
   Tom, again, I am curious as to whether or not you have any evidence
that the chlorine is actually harming the plants?
 
Ric
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