It's Alu, broh. U need to wipe it dry afterwards.
What about screen cleaning fluid? Is there no way of removing the stain?Tap water contains minerals and it will leave a stain after you use it. If you buy distilled water from grocery store and use that, it shouldnt stain.
the stain should come off and get some screen cleaning stufff.
never use water on the front screen just use mirco fiber cloth and screen cleaning it comes with a cloth
Post a pic. I use iklear to clean my idevices and Alu MacBook.