Trying my hand at brewing/fermenting. We drink lots of Crystal Geyser mineral water. They have 18oz and 32oz clear PETE bottles. Would these be ok to re-use for brew?
As far as oxygen permeation may be concerned, then yes they are okay.
You probably won't be able to carbonate in these bottles, unless the water in them is carbed. I cannot tell from the photo, if they aren't carbonated bottles, then you'd be better off using soda bottles.
I use those bottles for when I make 1 gallon batches for wine or mead for fermentation... then I switch to a 1 gallon glass jug from my LHBS for like 4.99
As cell stated, beer has hops in it, which will skunk if exposed to UV light for an extended time. Most homebrewers will stick with brown bottles for beer to protect against this. If you plan on keeping them in a dark place the entire time, I dont see a problem with them. You cont really have to worry about oxygenation unless you are going to be aging your beers in those for a prolonged time.
Two months ago I brewed my first batch. When I bottled, I only had once case of bottles. It was 10:30 at night & I had two more gallons of beer I did not intend to waste. Ran to the store & bought some 2-liter bottles of Sprite soda. Poured it out, rinsed, santized & bottled 3-two liter bottles. Not being dark bottles, I kept them in the pantry.
This last weekend we took the last 2 liter bottle of that first batch to a friends house & shared. It was divine!