Unscrew the aerator in the kichen sink. Then turn on the both faucets full blast for 15 minutes (have a rag for splahing.) Do the same in the bathroom and then the bathtub. Perhaps you can blow out the particles.
The larger ones are probably from pipe corrosion in the building, especially if the plumbing is old.
Nothing to lose with this simple technique and it will work or it won't.
Finale: clean the aerators well before you replace them...a pin helps, or just replace them, they are cheap at a dollar store.