Mystery Snails produce a lot of waste, so they require 2.5 gallons per adult snail (as babies you can be the judge of how much they need as they grow depending on the water quality). They can be in shallow or deeper water as long as the water is at least twice the shell height. I assume by "treated water" you meant that you used dechlorinator, which is good because as was stated metals (especially copper) are deadly to these guys. Salt (obviously) is also deadly, so if you have one in a tank with a Betta/any other fish make sure you don't use aquarium salt in that tank. Also, they will escape from any container that doesn't have a lid (I have personal experience with that) so make sure they can't get out. As a side note, I LOVE Mystery Snails and find them very entertaining, so I hope you enjoy these guys as much as I do. :)
Kindness and respect should be shown to all animals, no matter if they are furry, scaly, big, or small. Be a hero to the animals and GO VEGAN!