OrionGirl is right. Trout don't need spring water, but they do need cold clean water, as they have high oxygen requirements. Trout live in lakes, and that water isn't constantly moving. Well, I suppose it is, but not as much as a stream/river. It is very possible to keep trout in an aquarium, just harder than keeping tropical fish, as long as the water didn't get over 65°F and you had a strong filtration system. I would say a 250 gallon tank would be the minimum, although if you kept brook trout you could probably do a 175 since I don't think they get much longer than 20 inches, even in ideal conditions in the wild. Rainbow and brown trout seem to have a wider tolerance for water conditions though. I'm not sure how powerful of a chiller you would need to keep a tank that cool, but it would probably be rather expensive. Oh yeah, it would also be against the law to keep trout as pets in some states.