Understanding the Color of Tap Water

　　Investigating the Tint of Residential Water

　　What color does water present? Artists often portray water with a blue or aqua tone. Indeed, water displays blue-green shades, particularly in its depths, but within homes, it should appear clear. Water from the faucet ideally should not have a blue or greenish-blue tinge; such colors suggest contamination. Invisible microscopic particles can color the water. Colloidal suspensions, non-colloidal organic acids, and neutral salts also contribute to the water’s color change. This discoloration commonly stems from organic matter like decomposing leaves and aquatic plants. Water from swampy regions usually possesses the darkest hue, which however lightens over time due to sunlight and aging. All surface waters exhibit some coloration, and even some shallow wells, springs, and occasionally deep wells may exhibit discoloration. Typically, though, deep groundwater is almost transparent.

　　A standardized scale is used to measure the color intensity in water samples. A reading of 5 units indicates the water’s color is equivalent to that of distilled water with 5 milligrams of potassium chloroplatinate per liter. Highly colored water is generally undesirable for industrial applications due to potential staining. While color is not a significant concern for domestic use, it impacts the aesthetic quality of drinking water and can cause stains. The U.S. Environmental Protection Agency’s Secondary Drinking Water Regulations recommend that drinking water should have a color rating below 15 units. Color removal or reduction in water is commonly accomplished through coagulation, sedimentation, and filtration processes, with aluminum sulfate being the most commonly used coagulant. Methods such as superchlorination, activated carbon filtration, and potassium permanganate treatment have also been effective to varying degrees in removing color from water.