#PlantNanny is a very cute app! I've been using it for a few months, with only a brief pause recently to try a few new apps.

It's exactly the kind of light gamification that works for me. You water cute plants every time /you/ drink water, and the amounts are customizable. Your current plant wilts a little if you don't drink enough water, but I don't think they ever die.

It syncs to the Health app, which is very nice - a graph displays there as well.

I definitely recommend it.