Commorragh is a thirsty city, both literally and figuratively. The Dark City's population rivals that of many populated solar system and all of its resources must be imported. The Kabal of the Final Abyss is one group that is responsible for bringing in the billions of gallons of water to quench the thirst of the Dark City. They are currently in the final stages of draining the former ocean world of Kakou in an isolated Tau Sept. With the alien resistance broken and the world all but completely barren, they are preparing to move on to other perspective targets.
I bought a Dark Eldar army a few years ago, but ended up getting distracted by other projects and shelving it. A friend recently started his on DE army and it inspired me to drag my models out and put some paint on them. They are hardly the strongest army right now, but I like their designs and that's all I really needed. Besides I don't really have the money to be buying new models anyway so Its for the best that I paint what I already have.
Dark Eldar @ Games Workshop