The unupgraded version is balanced against a Cockatrice - it costs a little more, has 3 more HP, and hits for .2 damage more per round (taking the sleeping into account).
The upgraded version is balanced against an Abyss Crawler -- it costs a little more, so it has slightly better stats, and it's Life, not Water, so it's has a little something extra to represent Life's tendency toward better creatures than any other element.