Here's a thread on the kinds of plastics to avoid for fermenters:
https://www.homebrewtalk.com/threads/using-a-platics-water-bottle-7.228372/
Crazy enough the often bluish tinted water bottles typically used in water dispensers appear to be made of #7 plastic.
It may be OK for plain water use, but definitely
NOT when the beverage contains
alcohol.
#1 (PET) and #2 (HDPE) plastics are commonly accepted to be safe when used as fermenters.
Most
clear, highly transparent, plastic fermenters, such as "plastic" carboys (
Better Bottle knock-offs)
Fermonster,
Big Mouth Bubbler,
All-Rounder,
Fermzilla, etc. are #1 PET.
Most opaque white containers such as 3.5 or 6.5 gallon
Brew Buckets, 3-4 gallon buckets your local bakery gets their icing in, etc. are stamped #2, being HDPE, and safe to use as fermenters.
Avoid such vessels with color (such as orange Homer buckets). Colored #2
lids are probably fine, as they're not touching the alcohol containing beverages such as beer, cider, wine, etc.
If you don't have a well fitting (rubber) bung, use a piece of sanitized plastic or small-bubble wrap, wrapped several times around the airlock stem to make a "plug" for the opening. Then, for good measure, wrap a piece of sanitized plastic wrap around the neck and "bubble wrap plug" to "seal it off," to keep nasties out.
Once you know you're serious about homebrewing, get a copy of John Palmer's
How to Brew, 4th Edition.
And read/search Homebrew
Talk and ask questions to get the nitty gritty, and different opinions.