With this new power comes a weakness: the sea rejects the new Devil Fruit user and they become helpless while submerged in water (or "become a hammer," in Japanese parlance).[2] Oda stated in SBS that Devil Fruit users are susceptible to all types of water, not just seawater. This includes the white sea surrounding Skypiea. He elaborated on this, saying that "moving" water, like rain or waves, does not weaken Devil Fruit users, while standing water does.
Oda also said in SBS that it is not until a Devil Fruit user is knee deep in water that they become immobilized, this is seen with the Gorgon sisters and Luffy in Boa Hancock's bath. Brook was also seen slowly losing his strength as the water levels in the floods the Ryugu Palace, demonstrating that being in contact with the sea does not instantly rob their strength unless it reaches a certain level.