make tanks out of a plastic 5 g water jug, for like a water cooler. thats what i did for mine, though im not sure if a library would want somthing so DIY in the middle of the room
I hate to rain on your parade,but if the people who are keeping the betta in the library won't feed them,what makes you think they will do the necessary water chages in a unfiltered tank,bowl,glass,vase, etc.........
I doubt if they are doing water changes now,but bettas really do need a filter.
Here is some info I found http://www.petstoreabuse.com/betta.html http://fishlesscycling.com/articles/caring_for_bettas.html
That is what I plan on offering, they also have a 55g, I could offer to take over the maintenance for them.
If they refuse, then I will give them the page Lupie sent me and ope they do the right thing.
If they won't do the right thing by taking care of the bettas even after you give them a care sheet, I'd probably end up taking two jars with me to the library and stealing the bettas when no one's looking... >_>
Just remind them that they are "Gods" creatures too and being such need to be properly taken care of. If they can't do it, offer to take them home with you so that they can live healthy happy lives.