I suggest that you do not bother with a pvp build right -now-, as Mids hasn't been updated yet, and the set hasn't been nerfed thusfar. I've seen geyser on a blaster do well over 600 dmg in pvp. So, If I were you, I'd focus primarily on accolades, and incarnates, running with generic IOs, until we know for a fact that certain powers aren't being 'fixed', and you can sit down and figure out the best way to IO it with mids.
Although I'd like to lead with a pvp build (which would in all honesty get eviscerated since I'd be operating mostly under pve rules), I don't think I'm quite at the level to determine what's necessary for a successful Poison character. Does anyone run one regularly? I've seen that weaken is huge, and that generally it appears that around 47% accuracy from IOs is encouraged as well as maxed HP.
Aside from that is it just a few quick animating attacks and then straight survivability tools? I'd rather not begin a build, then realize just how offbase I was and have to double back around. At this stage I'm not sure if Water Blast has even been fully vetted for pvp.