most common cause of black particles showing up in tap water
is the disintegration of rubber materials used in plumbing
fixtures. These particles float and often adhere to sinks
and bathtubs and can appear sooty or greasy.
Gaskets, hoses connected to water heaters and washing machines,
rubber heat traps furnished with some newer water heaters
and o-rings can disintegrate over time and some pieces can
collect in tubs, toilet tanks, faucets and other locations.
Flexible hoses (braided stainless) are often lined with black
rubber. Homeowners should make sure they or their plumbers
select hose, gasket and water heater components that are compatible
with drinking water supply common to southern California.