My friend, John Balestrieri, has released Waterlogue for iOS.  Waterlogue is compatible with both the iPhone and iPad running iOS 7. From the press release:

We wanted to come up with an easy and fast way for people to create images based on the kinds of aesthetic decisions an artist makes when he or she is painting.

The technology we developed for Waterlogue transforms your photos into spontaneous, unique, and brilliant watercolor sketches that look like real paintings. Waterlogue distills your environment down to its essence—just the way an artist would—and turns even an on-the-fly snapshot into something luminous and sublime.

We designed Waterlogue to create the most authentic and aesthetically true watercolor interpretations available, and we hope that as soon as you start using the app, you’ll start seeing the world differently.

I've been playing with Waterlogue for a few days, and I have to say: This app advances the ability to easily create convincing watercolor art from photographs. John and Robert spent a year examining traditional watercolor and have created a deceptively simple app that faithfully replicates all of the hallmarks of its traditional counterpart.

At $3.99 from the App Store on iTunes, this software is a steal. John and Robert have indicated that Waterlogue will continue to evolve with additional features to be added over time. Highly Recommended!