If the particles are not showing up in the bottom of your toilets (which are connected to the cold water pipes) this is probably a hot water heater problem. You may need to flush out your water heater. When draining the water heater you will probably see a lot of debris coming out. When the water is heated, the small particles precipitate out and will settle in the bottom of the water heater. These particles can become agitated and be swept into hot water fixtures in your home.
It is recommended that a water heater be flushed every six months. Use caution when flushing your water heater as sometimes the debris in the tank can prevent the drain valve from fully closing. A licensed plumber can be helpful in resolving any issues you may have with your water heater.