Hi Alien
I've been using these water bottles to ferment wine in for years - nothing
wrong with plastic! My local home brew shop actually sells new and
identical bottles like those that contain water and charge a hell of a lot
of money for them - but the water ones come free!
Regarding the bung - the ones I use have a large screw cap which I keep
screwed on tight and drill a hole through it to accommodate the rubber
bung/airlock. A drill bit size of about 25mm should be about right (it'll
be one of those flat style drill bits).

Regards
"alien" > wrote in message
...
> I've been buying 5L bottles of spring water for making wine with and,
> well, just binning them afterwards. Instead of wasting them, how
> suitable would they be for fermenting in? They hold a bit more than my
> demijohns, so I thought I could rack them into demijohns for the first
> racking to avoid top up problems.
>
> My main concern is how airtight they'd be and how to fit the airlock.
> I've never seen a bung big enough for the mouth (about 5cm), but I'll
> check next time I'm in the local brew shop. I was thinking about using a
> rubber washer to help seal the lid, and maybe a rubber grommet to hold
> the airlock in place. Has anyone got any experience with this? I don't
> want to waste money on making wine in these if the containers will fail
> me. The bottle is made from PET and the cap from (about 1mm thick) HDPE.
>
> This would increase my capacity for wine making without massively
> increasing my expenses, which is always a good thing.