The Water type Starter Pokemon is the Bubble Frog Pokemon, Froakie. It evolves into Frogadier at level 16, who also has the same species. When it gains 20 more levels, it evolves into Greninja, the Ninja Pokemon. It gains a Dark type in addition to its Water type when it evolves into Greninja, making it even more effective against Delphox. However, this also makes it weak to Chesnaught.
Nothing too unique about this family either. It shares the same typing as Carvanha, Sharpedo, and Crawdaunt and it shares its hidden ability with Kecleon. Its signature move, Water Shuriken, can be used by Accelgor (Water Shuriken has increased priority and can hit multiple times). However, just like Delphox, it has some good qualities. It has the highest speed of all fully evolved Starter Pokemon and Water types. Its hidden ability allows it to change its typing if it uses a move of the same type, making it versatile.
Did you choose Froakie as your Starter Pokemon?