potassium reacts with water

The statement is false, because potassium is oxidized to potassium ion.

According to the equation:
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
and the half equation:
K(s) → K+(aq) + e-

Potassium is oxidized, because the oxidation number of K is increased from 0 (in K) to +1 (in K+/KOH), or because electrons are released.