just because its new and you have never had water in it
doesn't mean the factory didn't run water through it. They more than likely filled hw heater to check operation.
Also if you had a good dealer he should have also ran water through it.
During pdi then should have ran water in the system to show you operations such as
water pump,hw heater,toilet,faucets, and showers.
when they install all the plumbing who knows what saw dust
And plastic particles are in those lines only to be flushed to your strainers.
did they show you were your water filter was?
Take a look at the bottom of the filter canister and see if there's not allready sediments there.
Good luck! Happy camping