@Paige *******
if you have a valid extension, supported by attending a real uni here, don't worry. Just get a new passport, as you said, even if readable, when water damaged it's no good. Then just show both the old, invalidated passport (snipped/holed/whatever they do to an American passport to mark that), and the new passport at passport control. Just explain its new and old passports. Hand over showing the page with the reentry stamp maybe. They will see it in their system too and just stamp your new passport with a "stay until" date, that will be the expiry date of your current one year stamp. After that, after arriving in Thailand, you go to the immigration office that gave you that stamp, and get it transferred to the new passport.