Stuff in water lines

We have a 2011 Outback and have noticed little bits of what appear to be plastic about the size of grains of play sand getting caught in the aerator in the kitchen sink. The lavatory, toilet and shower don't seem to catch as much as the sink, but do catch a tiny amount. I don't notice it when running off the pump, just the city supply. I don't use a filter and have noticed it in several parts of the country, so it is not limited to one park or area. Any idears?