It's a common problem in an RV. The water heater and "hard" water or perhaps the mixing of water from different sources causes calcium compounds to precipitate out and clog shower heads, faucet aerators, and the toilet bowl ball valve.
Soaking in vinegar often does the trick. But, sometimes you have to mechanically get the crud out.
Alex
"There is a cult of ignorance in the United States, and there has always been. The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that "my ignorance is just as good as your knowledge."
-- Isaac Asimov