water tank set to too low a temperature. This usually has a strong sulfur or rotten egg (S) odor and is easily corrected by draining the water heater and increasing the temperature to or higher. The odor will always be in the hot water pipes if sulfate reducing bacteria are the cause and never in the cold water plumbing. Learning the water impurity indication color spectrum can make identifying and solving cosmetic, bacteriological and chemical problems easier. Water quality and color The presence of color in water does not necessarily indicate that the water is not drinkable. Water with high water clarity is generally more cyan in color due to low concentrations of particles and/or dissolved substances. Color-causing particulate substances can be easily removed by filtration. Color-causing dissolved substances such as tannins are only toxic to animals in large concentration. Color from dissolved substances is not removed by typical water filters; however the use of coagulants may succeed in trapping the color-causing compounds within the resulting precipitate. Other factors can affect the color seen: Particles and solutes can absorb light, as in tea or coffee. Green algae in rivers and streams often lend a blue-green color. The Red Sea has occasional blooms of red Trichodesmium erythraeum algae. Particles in water can scatter light. The Colorado River is often muddy red because of suspended reddish silt in the water. Some mountain lakes and streams with finely ground rock, such as glacial flour, are turquoise. Light scattering by suspended matter is required in order that the blue light produced by water's absorption can return to the surface and be observed. Such scattering can also shift the spectrum of the emerging photons toward the green, a color often seen when water laden with suspended particles is observed. Color names Various cultures divide the semantic field of colors differently from the English language usage and some do not distinguish between blue and green in the same way. An example is Welsh where can mean blue or green, or Vietnamese where likewise can mean either. Conversely, in Russian and some other languages, there is no single word for blue, but rather different words for light blue (, ) and dark blue (, ).*research needed: “light blue” may refer to “cyan* Other color names assigned to bodies of water are sea green and ultramarine blue. Unusual oceanic colorings have given rise to the terms red tide