Just to play devils advocate for a moment;
Our tap water is chlorinated, ergo our tap water should not have the bacterium for legionnaires disease in it.
I know that our pure water has all the chlorine removed, but surely the water will have to have the bacterium in for it to multiply? It can't spontaneously create itself can it.
Now there are many thousands of us using WFP and have been for years, and so far there have been zero incidents of Legionnaires disease caused through WFP useage.
Now I know that this does not mean it is impossible, but the chances of it happening must be incredibly low.
This doesn't mean that we shouldn't take great care of our equipment, changing our prefilters regularly, and with this being done the chances of the bug growing are even slimmer.
Argumentative bit over
You are right about pure water absorbing carbon dioxide from the air, our pure water very soon becomes a very mild carbonic acid
But this doesn't affect the purity of the water.
The pure water will of course try and absorb whatever it can from the atmosphere, but that is completely piddling so far as we are concerned.
It takes a lot for the limestone to disolve into our water to effect the TDS reading!
My plastic wheelbarrow, the inside of which had a layer of grime and muck on had partly filled over a few days with rainwater.
I checked the TDS, and even with bits floating around in it, the reading was still 0.000 pmm.
I was quite surprised about this!
So I cleaned it out, scrubbed it clean and rinsed it out with some pure water.
A couple of days later there was another couple of inches of rainwater in it, this time the TDS reading was 0.003 ppm. though there was more in the way of leaf detrius floating around in there.
Conclusion??
Well I think that the water we use to clean windows is only really affected by truly disolved solids i.e. what gets into the water after it has been filtered through various strata as it makes it's way down to the water table.
In the lab utter purity would be essential, whatever the water may absorb from the atmosphere won't affect us though, we store it in sealed containers too.
Another interesting property of very pure water is that it's freezing point is well below 0 degrees C.
Clean out a little shot glass thoroughly, rinse well with your pure water and then fill it with the pure & put it in the freezer.
Do the same with just an ordinary glass of tap water.
Even with our pure window cleaning water, providing you check on it often, will become ice quite a while after the ordinary tap water.
When it's frozen solid, pick then up and compare the ice formation.
The pure water paterns are far smoother than the tap water ones....
Yeah, ok, I'm sad, and I've no idea why I try these pointless little experiments, they just amuse me
Regards,
Ian