Pure H₂O is only part of the story. Natural and drinking water contains dissolved ions and gases. Calcium and magnesium contribute to hardness; bicarbonate often matters for alkalinity; sodium, chloride and sulfate may also be present.
That chemistry explains ordinary observations. Limescale in a kettle is mainly linked to calcium carbonate deposits. Mineral content changes taste and electrical conductivity too.
Water itself is unusual: ordinary ice is less dense than liquid water, it stores a lot of heat for its mass, and its polarity makes it an excellent solvent for many ionic and polar substances.