Water can take on different colors depending on what is dissolved in it. While pure water is colorless, the presence of minerals and other substances can give it various tints and hues. One of the most commonly observed colors of water is blue. But what causes water to turn blue? The blue color of water is primarily due to the presence of calcium carbonate. Let’s take a closer look at how this common mineral makes its way into water sources and gives them their characteristic blue tint.
The Role of Calcium Carbonate
Calcium carbonate (CaCO3) is one of the most abundant minerals on Earth. It is found in rocks such as limestone, marble, and chalk. When these rocks weather and erode, calcium carbonate dissolves into the water. Once dissolved, the calcium carbonate molecules scatter and absorb light, giving the water a blue-green color. The more calcium carbonate that is present, the deeper the blue hue becomes.
This effect can be easily observed in nature at blue lakes or blue grottoes. These geological formations occur when water encounters limestone rich in calcium carbonate. As the mineral dissolves into the water, the blue tint becomes distinctly visible. Some well-known examples are the Blue Grotto sea cave in Italy and Blue Lake in New Zealand.
Light Scattering
The specific reason that calcium carbonate causes water to turn blue relates to the principles of light scattering. Light is made up of different wavelengths across the color spectrum. When light hits molecules in water, some wavelengths get absorbed while others get scattered. The scattered blue wavelengths are what give water its azure appearance.
Calcium carbonate molecules enhance this light scattering effect because of their small size. The fine particles diffuse and reflect the short wavelengths of blue and green light. Meanwhile, the longer wavelengths at the red end of the spectrum are absorbed rather than scattered. The cumulative effect is that the blue hue becomes the most visible color remaining.
Interestingly, water rich in calcium carbonate often exhibits an even stronger blue-green color when viewed from above. This is because the scattering effect is reinforced when light has to pass through more thicknesses of water. The blue color becomes further accentuated and concentrated.
Factors That Influence Color
The degree to which calcium carbonate makes water appear blue can vary based on several factors:
Concentration – Higher amounts of dissolved calcium carbonate result in a more intense blue color. Lakes and pools with very low mineral content will appear only faintly blue.
Suspended particles – Sediment or organic materials suspended in the water can mute or block the blue hues. Glacial meltwater often has a grey or cloudy appearance because of suspended rock flour.
Water depth – In deep, clear water, the blue color is enhanced as more light gets scattered through longer pathways. Shallow waters appear greener or lighter blue.
Viewing angle – Looking at the water from directly above accentuates the blue scatter effect compared to viewing it at a slanted angle.
Time of day – The color may appear different depending on the angle of sunlight and associated changes in light intensity.
| Calcium Carbonate Concentration | Water Color |
|---|---|
| Low | Pale blue |
| Moderate | Blue-green |
| High | Intense blue |
This table summarizes how higher calcium carbonate concentrations lead to a more vibrant blue color in water.
Other Blue Water Examples
While calcium carbonate is the primary contributor to blue colored water, there are some other examples where minerals cause similar effects:
– Copper minerals – Dissolved copper from rocks or soil may impart a blue-green hue, often seen in mineral hot springs. The vivid blue colors of Arizona’s Havasu Falls are due to dissolved copper.
– Algae blooms – Blue-green algae contain a pigment called phycocyanin that can give water a distinct blue-green tint when algae populations are very high.
– Hydrogen sulfide – Volcanic vents and sulfur springs emit hydrogen sulfide gas, which reacts with water to form microscopic sulfur particles that scatter blue light. Examples are the bright blue water at the Ice Lakes in Canada.
However, these mechanisms are less common than the ubiquitous presence of calcium carbonate minerals. In most lakes, pools, springs, and oceans, calcium carbonate remains the predominant chemical contributor to blue water color.
Conclusion
The next time you see a beautiful blue lake or sea, you can thank calcium carbonate for creating that scenic color. Water’s ability to dissolve this mineral plays an essential role in determining natural water color. The small size of calcium carbonate particles combined with the optical scattering of blue wavelengths gives water its azure blue hues. Higher concentrations and deeper thicknesses of water further enhance this effect. So a vibrant blue color is a good indicator of abundant calcium carbonate that has dissolved into the water source. When appreciated through the lens of science, these blue bodies of water take on an even more marvelous appearance.
