By leveling up, Feraligatr learns Hydro Pump at different levels for each generation.
In Generation II (Gold, Silver, Crystal), Feraligatr learns Hydro Pump at level 58.
In Generation III (Ruby, Sapphire, Emerald, FireRed, LeafGreen), Feraligatr learns Hydro Pump at level 55.
In Pokémon Diamond and Pearl, Feraligatr learns Hydro Pump at level 63.
In Pokémon Platinum, HeartGold and SoulSilver, Feraligatr learns Hydro Pump at level 71.
In Generation V (Black, White), Feraligatr learns Hydro Pump at level 76.
No, Dragonite cannot learn Hydro Pump.
Floatzel cannot learn Hydro Pump.
Quagsire cannot learn Hydro Pump.
Azumarill learn Hydro Pump at level 57.
At level 40, Kingdra is suposed to learn Hydro Pump.
Swampert does not learn Hydro Pump.
No, Floatzel does not, and cannot learn Hydro Pump without the use of hacking.
Floatzel cannot learn Hydro Pump without the use of hacking.
It learns Hydro Pump at level 48.
blastoise learns hydro pump at 63
Floatzel cannot learn Hydro Pump in any of the Pokémon games as of Generation V.
Well, it's actually Hydro Pump, but Jellicent can learn it at level 53.