This would be the Waterbearer version series.
First issue February 2003 by Rick Veitch.
Best stories from this series are around issue where the American Tidal storyline takes place.
Also check his appearances in JLA Classified.
Although he was equally impressive (beating class 100 characters and stuff) in his previous series when Peter David was writing the book (issues 1-49) and his appearances in Grant Morrison's JLA in the same period.
Manhandling Despero who previously owned Martian Manhunter (until he turned to telepathy and won...)
Lifting an entire city block underwater (not a building the ENTIRE STREET with trees, cars, etc)
Lifting an 8 store building outside water
Taging and keeping up with Flash.
Outrunning angels
Being faster than Deathstroke
Swimming at 1000 knots
Swimming at 20000 feet per second (!!!)
Witstanding blasts that KOed Orion.
Dropping from a veeery high building (something like 20 stores) without trouble.
Jumping 500 feet from out of water and blitzing a demigod
Controlling entire Tidal Waves
Owning the Deep Six (class 100 Apokolips New Gods)
Killing an Imperiex Probe (the ones that killed Guy Gardner and Hipolyta)
Beating Olympian (out of Water)
Battling the Fire Elemental of Earth without any problems from the fire
Battling Ultraman
Stalemating an entire JLA team (and taking punches form an enraged Wonder Woman)
Beating Power Ring (evil GL)
Beating Kyle Rayner (underwater)
Stalemating Lobo
Owing via Telepathy a dragon that was toying with Power Girl
Breaking through steel doors while infected with a virus that took out Flash.
Fighting an entire alien army (and beating his leader)
Beating Tempest at one point or another.
Undoing spells that Manitu Raven couldn't
Using the Water Hand to disable stuff inside someone's brain.
Being only mildly affected by bullets (scrathes on his skin at most)
Etc.
The list is very long.
Plus you can also see the training he had with the JLA
Plus he had 2 power upgrades
1. When Poseidon gave him a portion of his power
2. When the lady of the lake gave him the water hand