The plastic (PET #2) water jugs are probably okay for a single use, but I seem to remember seeing a promo for some "are you at risk?" local news report on how water bottles should not be reused. I guessed that it was do to microbial contamination build-up which would not be a problem for a single use in brewing.
I brewed Denny's Rye IPA and a saison last summer, trying 5 or 9 yeast strains for each respective batch. Glass gallon jugs worked great, but don't fill them more than 1/2 full, or to the shoulder if you are using anti-foam. I only had a couple jugs foam over. There is relatively a lot of beer lost in transfer so you only end up with a six-pack from each ferment.