I've posted something like this before but I want to bring it up again. Anyway, I know that the Waterworks gear is worth it... But I've finish it over 10 times, and no gear. Also, I'd really like the hat. So what enemy drops it?
Usually by the fifth or so run, one would start to see drops being collected.
Having done it over ten times as you said and not having at least one part of the gear is quite odd.
Luska Charmbeak, the first boss you encounter in the dungeon is the one that drops the hat.
The robe and shoes are dropped by the final boss.
Also, remember (especially at your level), you've other, better alternatives such as your level 76 Crafted Hat (Poet's Hood) available from Lewelyn in Dun Dora, Avalon along with your level 74 crafted robe (Armor of the Banneret)
You can also opted for your Ziz-Zag Gear by running that Dungeon.
My myth, I believe, had to farm it for 3 weeks to get all the gear he wanted. Not knowing your situation, I will suggest getting the Wintertusk crafted gear. It's similar to WW gear, and it's guaranteed because you craft it. I usually run a combo of WT hat and WW boots and robe. While an old article, it's my go to for information. CLICK ME to go to the Wizard101 Central guide on waterworks drops
on balance, i got all 3 pieces in 2 runs on storm, i got boots in 1 run, took about 20 runs to get robe, and never got hat (went on to avalon, used avalon crafted, then khrys crafted, then cabal hat) currently on fire after 3 runs, got hat and boots.