Re: FILYERING TAP WATER FOR FRESH WATER TANKS ?

On Wed, 15 Oct 2003 15:02:52 UTC, [EMAIL PROTECTED] (Gary V. 
Deutschmann, Sr.) wrote:

> Water is the worlds most universal solvent.
> So in essence, whether it comes from your tap or has been filtered
> until perfectly clean, I guess it could be considered a corrosive.
> But I wouldn't say 'clean' water is much more corrosive than 'dirty'
> water, but I'm sure it is by a minute degree.
>

The reason for the claim that it's very corrosive seems to be this:

The water from your tap probably has carbonate to the extent of a few 
German units (KH), and has a pH up in the 7s or above.  If the natural 
source is softer than that, water companies generally add carbonate; in 
many places that's unnecessary.  They treat the water in this way because 
really pure soft water, with no buffering power, will turn slightly acidic
as it picks up CO2 from the air.  And it will gradually corrode pipes, and
the water company really doesn't like this.  It may also leach enough 
unpleasant metals from the pipes (lead, cadmium) to be a health hazard.

So, you purify your water, and you take that nice carbonate out.   As CO2 
dissolves in the pure water, you have something that is very slightly and 
slowly corrosive, and you must not store it in your usual lead-and-cadmium
containers.  Or anything else metallic.  Glass, though, is really good 
with mild acids over a reasonable time; so are plastics that are certified
for use with food and drink.  If your container holds orange juice without
rotting, you don't have to worry a lot about pure water.

Am I understating the corrosivenss a little?  Does anyone *know*?  Anyway,
I'm not kidding about orange juice (citric acid in such concentration that
you can taste it) versus pure water (much lower concentartion of a weaker 
acid).

-- 
Dan Drake
[EMAIL PROTECTED]
http://www.dandrake.com

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