Potassium permanganate turns purple in water due to the following reasons:

* Manganese in the +7 oxidation state: Potassium permanganate contains manganese in its highest oxidation state (+7). This highly oxidized manganese ion is responsible for the intense purple color.

* Absorption of light: The purple color arises from the absorption of specific wavelengths of light by the permanganate ion (MnO4-). It primarily absorbs yellow and green light, transmitting the complementary colors (blue and red), which combine to create the purple hue we see.

* Formation of permanganate ions: When potassium permanganate dissolves in water, it dissociates into potassium ions (K+) and permanganate ions (MnO4-). These permanganate ions are the ones responsible for the purple color.

In summary, the purple color of potassium permanganate in water is a result of the highly oxidized manganese ion's ability to absorb specific wavelengths of light, creating a purple appearance.