Re: removing chlorine or chloramine from municipal tap water.
- From: robert bristow-johnson <rbj@xxxxxxxxxxxxxxxxxxxx>
- Date: Sat, 27 Jun 2009 17:11:32 -0700 (PDT)
On Jun 27, 1:51 pm, "N:dlzc D:aol T:com \(dlzc\)" <dl...@xxxxxxx>
wrote:
"robert bristow-johnson" <r...@xxxxxxxxxxxxxxxxxxxx> wrote in
messagenews:e5cc4829-4af7-4a79-b89a-1bf8386f9b5b@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
hi, i haven't been here to sci.chem, but i have
a question or two that i am seeking authoritative
answers (i get inconsistent answers from what i
gather on the web). from what i have gathered
so far:
1. nearly all municipal water systems chlorinate
the water supply to disinfect and protect it from
pathogens in transit.
... and to disallow pathogens growing in the distribution system.
that's what i meant by "in transit".
however, when i lived in Portland Maine in the
early 90s, i was told that the water they had
from Sebago Lake was so good, it didn't need
it and some people actually used the tap water
in lieu of distilled water in some applications
including the lead-acid car batteries of the day.
Rose Water district in Arizona. Well water, really pure. Until
the system got infected, and children died form organisms
entering their eyes when they washed their faces.
this killed some kids??!! there must have been hell to pay (by some
municipal or water district officials) for that.
2. some municipal water systems chlorinate
by use of chlorine gas, others do it with mono-
chloramine, which i read is a compound
involving Cl and NH3. are there other methods
widely used, or are these two the main methods
used with municipal water in the U.S.
Liquid chlorine (bleach).
Free chlorine generated in much the same way the pool tablets work.
Chlroine and other oxidants generated from brine and electricity.
3. i have read that one step one can use to
remove or decrease the level of chlorine is to
fill a clean and open-top container with tap
water and let it set with the top open for a few
hours or overnight. is this true?
Yes.
that's nice to have verified. thanks.
and if so, how long need it sit?
Aerate it, that will take out about 50%.
how long to take out 50%? 3 days? (no, that would be 3 days inside
the pipes.) is overnight enough? or 1 hour?
Add a lemon wedge,
that will kill all of it.
but "killing" the chlorine is not the same as removing it. does it
precipitate or remain in solution, but in a combined or non-reactive
state?
how about a few drops of ReaLemon (per gallon)? or a few drops of
plain, white vinegar?
will any of these acids work with mono-chloramine?
if it's an exponential thing, does anyone
have an idea for how long it needs to sit to
reduce the concentration of Cl to 1/2 of the
previous level?
Chlorine in the distribution system has a half-life of about 3
days (depending on water temp and system cleanliness). Ambient
light decreases this, and aerations does too.
4. does this technique above work with water
treated with mono-chloramine as well as with
water treated with chlorine gas?
No.
okay, that is useful information. it seems to me that, municipalities
might serve their constituencies better to use chlorine gas (or Cl2
dissolved in liquid, however it is added) over mono-chloramine in
their chlorination process.
5. how well do Brita water filters do in removing
chlorine or mono-chloramine?
Fine. Passing through the carbon, the carbon is sacrificial.
Essentially no chlor-____ makes it past the carbon when it is
fresh.
i guess that's how they get their market. i sometimes worry about
things that get sold that are either ineffective or without a real
need or basis for it.
if teamed up with the "setting" method above,
does that work better than just passing fresh
tap water through the filter? does it make no
difference?
No difference. Because this sitting usually happens in a
refrigerator, which slows all reactions down.
well, i didn't intend to imply that this uncovered "sitting" happen in
a refrigerator, but in a pitcher or some other uncovered container at
room temperature (the water would be slowly warming from tap
temperature to room temp). i know that if it sits there for weeks,
some algae or mildew or something might grow in it. but overnight
seems safe, no? periodically, this container should be washed, of
course.
if some of the chlorine is removed by aeration, does that not mean
that the carbon in the Brita filters absorb less chlorine and take
longer to be "spent" (opposite of "fresh"), to get to a state where
the absorbtion of chlorine is inhibited because it has reached its
capacity?
thanks, David, for your response. i hope you don't mind if i continue
to flesh out these issues, because i am hearing some mixture of truth
(at least what you verified) and urban myth, i think.
BTW, my interest is only in good drinking water (or tea-brewing
water). this is not about dechlorinating water for aquariums and
fish. that's where i see all of the discussion on the web and they're
talking about adding some *other* additive. i only seek to *remove*
stuff (like chlorine), not add stuff, but i might add a very small
amount lemon or vinegar to neutralize chlorine.
r b-j
.
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