Bacterial Growth in Water Reservoirs

[HW Mueller]

Victor,
I was only surprised at your "5% alcohol OR MORE".
Perhaps it was just unfortunate that I got this mentioned bottle in my hand, I have had stuff standing around with much lower organics, without bugs. Anyway, if a closed bottle didn´t develop any microbes after a few weeks it´s unlikely they ever will, as long as even H2O or MeOH, etc., molecules won´t even get in or out.
That´s why I collect Milli Q water in 2.5L bottles with teflon caps, place them in a cold room, and UV test them (in a detector), before use. Record: About one year without UV deterioration (or chromatographic change). The outlet of water prep apparatus can be kept clean over many month by using a hose which is big enough to loose the water (and dry) up to the filter afer use, also one should discarding the first few liters after re-use.
Tom,
I am not sure that I understand all of that, but the decrease in allowable storage time was not due to frits that became more and more dirty, etc.?

[tom jupille]

However, do you have real evidence that bugs can grow in 5% ACN? It seems that several posters here have no evidence that this can occur, despite the hypothesis that it might be a carbon source.

You're right. The consensus seems to be that 5% of MeOH or ACN are at least *static (to steal Bruce's term).

The paranoid part of my brain, however, says that someday, somewhere, a mutant bug will develop that likes 5% ACN.

[HW Mueller]

I agree on that, as mentioned before, we have a lot of genious around that will manage that, just as with antibiotics where it took quite some experts to misuse them, host the resulting bugs, and on top of this spread them to others, worldwide.
Meanwhile, to the 5% I would add cleanliness (sometimes clean filtration, certainly tight caps on bottles, opening them as little as possible, keep them cold, and avoid any plumbing especially that which is partially open to the atmosphere).