Urban water systems contain impurities mainly composed of mineral salts such as calcium, phosphates, nitrates, sodium, potassium and chlorine. If you spray untreated water, the water will leave white traces while drying, due to mineral salts contained in the water that remain apparent on the surface after evaporation.
Pure water is obtained by filtration and purification so that impurities and all mineral salts are completely eliminated, it is then exclusively composed of H2O molecules. This operation is carried out by specialized equipment and the process is called “Reverse osmosis”.