Not by leveling up. But probably from TM though.
Azumarill learn Hydro Pump at level 57.
At level 40, Kingdra is suposed to learn Hydro Pump.
Swampert does not learn Hydro Pump.
Seadra learns hydro pump at level 40.
Milotic learns Hydro Pump at Level 40.
Croconaw learns Hydro Pump at level 51.
blastoise learns hydro pump at level 44
Samurott learns Hydro Pump at level 62.
Empoleon Learns Hydro Pump At level 59/ 99Lloyd99
Marshtomp is an evolved form of Mudkip, who learns hydro pump at level 42.
It learns Hydro Pump at level 48.