The resin used in some home water softeners is comprised of small, round, plastic-looking beads. This is the material that is used to remove the hardness from your water. If you see these in your sink, it probably indicates that the screen used to keep them in the softener is cracked or broken. Have your water softener serviced.
More information can be found at the Environmental Protection Agency’s website at http://www.epa.gov/safewater/faq/faq.html