If you're referring to "water cooler" style bottles, it's probably not a good idea to use that as a fermenter. First - unless you can confirm with the bottle manufacturer that the material won't break down from cleaning or sanitizing solutions...or allow O2 to permeate the bottle, you're taking a good risk of making really bad beer. Second - there are way too many "nooks and crannies" to clean and sanitize in the "water cooler" bottles I'm familiar with. IMO - spend a couple extra bucks ($25 +/-) and get a fermenting bucket, carboy etc. with smooth surfaces (on the inside). Your fermenter needs to be cleaner than clean and completely sanitized. It's really impossible to ensure a vessel is clean and sanitized if it has lots of places for bad critters to hide - "nooks and crannies".