I would go to walmart or another kitchen type store and get a 2-3 gallon cookie jar...sneak that in...(they're about 9-10 dollars usually)They will never expect it to be for a fish...


They have some 2 gallon cookie jars at walmart...I almost got one for my fish but i ended up going with a critter keeper...
There are a few people on here that use these.
I would also suggest using tap water and a good water conditioner like prime...A lot of times spring water can lack minerals and stuff that are good for fish. They also make water conditioners just for bettas...I havent ttried any of the betta type conditioners though..I usually just use prime.
You dont need a filter for a tank this small...you just need to keep up with water changes so that ammonia doesnt build up...In a tank 1 galon or smaller I do 100% water changes daily.