The halacha (SA OC 318) generally is that if someone cooks food b'mezid (on purpose) on Shabas then he may not eat it, not even after Shabas.
Magen Avraham adds that the pot in which the food was cooked is non-kosher also. Later authorities explain that it is non-kosher for that person: anyone else can eat what may be cooked in it on a future date, but not him. (It can, incidentally, be made kosher again by the usual means (Kaf Hachayim).) They also mention that the ban on eating the food applies even to plain water that was cooked.
Mishna Brura explains that the reason the pot in which food was cooked is non-kosher (to him) is that it absorbed the forbidden (to him) food.
Now, normally, absorption is a problem because the taste of the non-kosher food is absorbed in the walls of the pot, and comes out again when the pot is next used. Seemingly, then, if one cooked plain water on Shabas, the pot should not be rendered non-kosher: after all, water has no taste.
Do any pos'kim discuss this issue: whether a pot in which plain water was cooked on Shabas is rendered non-kosher for the one who cooked in it? Or can anyone offer arguments one way or the other (beyond what I've written above)?
Someone raised this question at the Shabas table this week, and I figured I'd bring it here.