What color is water?
Ordinarily we think of water as being blue in color. When artists paint bodies of water they generally color them blue or blue-green. While water does reflect blue-green light, noticeable in great depths, it should appear colorless as used in the home.
Ideally, water from the tap is not blue or blue-green. If such is the case, there are certain foreign substances in the water. Infinitely small microscopic particles add color to water. Colloidal suspensions and noncolloidal organic acids as well as neutral salts also affect the color of water. The color in water is primarily of vegetable origin and is extracted from leaves and aquatic plants. Naturally water draining from swamps has the most intense coloring. The bleaching action of sunlight plus the aging of water gradually dissipates this color, however. All surface waters possess some degree of color. Likewise, some shallow wells, springs and an occasional deep well can contain noticeable coloring. In general, however, water from deep wells is practically colorless.
An arbitrary standard scale has been developed for measuring color intensity in water samples. When a water is rated as having a color of 5 units, it means: the color of this water is equal in intensity to the color of distilled water containing 5 milligrams of platinum as potassium chloroplatinate per liter. Highly colored water is objectionable for most process work in the industrial field because excessive color causes stains. And while color is not a factor of great concern in relation to household applications, excessive color lacks appeal from an esthetic standpoint in a potable water. Further, it can cause staining. U.S. EPA Secondary Drinking Water Regulations recommend that a potable water possess color of less than 15 units. In general, color is reduced or removed from water through the use of coagulation, settling and filtration techniques. Aluminum sulfate is the most widely used coagulant for this purpose. Superchlorination, activated carbon filters and potassium permanganate have been used with varying degrees of success in removing color.