New hot water faucet rusting out

Hello,
I replaced the powder room sink faucets a few weeks ago and noticed some discoloration.
It appears that the hot water faucet is rusting away.
I have a water softener system installed and the cold water faucet seems ok.
The only thing i did was connect the water supply lines to the new faucets.
any ideas what is causing this?
thanks for any insight/advice

 

Is it a steel washer? Are the water supply lines copper, plastic or a metal flex lines? The way the rust stains spread out, it just could be water getting under the escutcheons. Clean the sink top and put a bead of caulking on the edge of the escutcheons, press it down on the sink top and wipe away excess caulk. Why just the hot side?

I searched on "brass washers" and there are a lot of brass washers listed. You might want to replace these with brass.

 

Thanks for getting back to me.
Water lines are copper. There is a shut off valve, from the valve i used new metal flex lines to the faucet. I took the escutcheon off of the cold side and the cold side has a little rust as well.

 

Faucets should never have steel washers in water contact areas.

 

The brass nut should not be tarnished that fast if it was a few weeks ago. The rusting washer seem to have an anodized coating that has deteriorated. It maybe an electrolysis going on, it way I asked what the water lines were made of. The top knurls for the handle also shows electrolysis (green). Its hard to believe it is all this in just a few weeks. This was a brand new faucet? What brand may I ask?