Well, instead of asking us you have to carefully analyze your environment and find source of this type of particles. It might be even something as stupid as dust on your sleeve brought from outside. I am not quite sure if this thing happened once or it is a constant annoyance. I would examine everything from the bulk loader to the camera inside, all the storage places etc. Water is the last place. Even if it carries some particles they should get lost, when you shake the film from the access of the water. However, if you use films like Foma, Shanghai or Lucky such a perticles may be included in emulsion already in production stage.