We noticed a few days ago that our water looked dirty and had a yellow-brown tinge to it. We called a plumber in who said it was our water heater, which was rusted at the bottom and slightly leaking (although only 4 years old). We had a new one installed today and tonight as I was filling the tub to give our kids a bath I noticed it still looks dirty! How can that be if the heater is brand new? Could it be something else? I have no idea where to start here...
BTW Our pipes are copper and none of our neighbors are having this problem.
Thanks for any answers...

Could be water that was left in lines from old water heater. Not all the water would drain out while switching out the old. Let the hot water run for 15 min or so to flush the lines out..

I agree, run there water for 20 minutes to see if it clears up. Try the cold, is it rusty too?

Thnaks guys, it does seem to have cleared up after running it for a bit. I was beginning to worry that this was about to become very expensive...