Sediment/flakes in hot water
If you have a tank-type heater, flush the tank.
Beware that if the tank drain has not been used, it may fail to seal well after being used to flush the tank (so try to schedule the operation for when the stores are open and you can go get another one.)
A water softener (at least on the supply to the water heater) is probably advisable since you have hard water from the city, and heating it tends to cause stuff to come out of solution. Your flakes are mostly limestone (calcium carbonate, dissolved in the water, which comes out of solution as the water is heated), in most parts of the world.