Dissolved organic matter (DOM) is the primary cause of color in natural waters. DOM consists of a complex mixture of organic compounds, including humic substances, fulvic acids, and lignin, which are derived from the decomposition of plant and animal matter.

Humic substances are the major contributors to color in natural waters. They are a complex mixture of organic compounds that are formed during the decomposition of plant and animal matter. Humic substances are dark brown or black in color and have a high molecular weight.

Color and DOC are positively correlated in natural waters. This means that as the concentration of DOC increases, the color of the water also increases. This is because DOC is a major component of DOM, which is the primary cause of color in natural waters.

Color can have a number of negative impacts on aquatic ecosystems. These impacts include reduced light penetration, which can inhibit photosynthesis and primary production; increased water temperature, which can stress aquatic organisms; and decreased dissolved oxygen levels, which can lead to fish kills and other problems.

There are a number of common methods for measuring color in water. These methods include the platinum-cobalt method, spectrophotometry, and fluorometry. The platinum-cobalt method is a visual comparison method that involves comparing the color of a water sample to a series of standards. Spectrophotometry is a method that measures the amount of light that is absorbed by a water sample at a specific wavelength. Fluorometry is a method that measures the amount of light that is emitted by a water sample when it is exposed to ultraviolet light.

The color of water can be affected by a number of factors, including the type of DOM present, the concentration of DOM, the pH of the water, and the temperature of the water. Different types of DOM can produce different colors. The concentration of DOM can also affect the color of water, with higher concentrations of DOM resulting in darker colors. The pH of the water can also affect the color of water, with lower pH values resulting in darker colors. The temperature of the water can also affect the color of water, with higher temperatures resulting in lighter colors.

Color in water can come from both natural and anthropogenic sources. Natural sources of color include DOM from decomposing plants and animals, as well as minerals and metals. Anthropogenic sources of color include industrial discharges, agricultural runoff, and sewage treatment plant effluent.

There is no evidence that color in drinking water has any adverse health effects. In fact, some studies have even suggested that color in drinking water may be beneficial for health. For example, one study found that people who drank water with a high concentration of DOM had a lower risk of heart disease.

Color in drinking water can have a number of aesthetic effects, including unpleasant taste and odor, discolored teeth, and staining of laundry and fixtures. These aesthetic effects can make water unappealing to consumers and can lead to complaints.

There are a number of methods that can be used to remove color from water. These methods include coagulation and filtration, activated carbon adsorption, and reverse osmosis. Coagulation and filtration is a process that involves adding a chemical coagulant to the water, which causes the DOM to form flocs. The flocs are then removed from the water by filtration. Activated carbon adsorption is a process that involves passing the water through a bed of activated carbon, which adsorbs the DOM. Reverse osmosis is a process that uses a semipermeable membrane to separate the DOM from the water.

There are a number of challenges associated with removing color from water. These challenges include the cost of treatment, the effectiveness of treatment, and the potential for the formation of disinfection byproducts. The cost of treatment can be a significant barrier to the implementation of color removal technologies. The effectiveness of treatment can also be a challenge, as some types of DOM are more difficult to remove than others. The potential for the formation of disinfection byproducts is also a concern, as some of the chemicals used to remove color from water can react with disinfectants to form harmful byproducts.

There are a number of emerging technologies for removing color from water. These technologies include advanced oxidation processes, membrane filtration, and ion exchange. Advanced oxidation processes are a group of technologies that use hydroxyl radicals to oxidize and mineralize DOM. Membrane filtration is a process that uses a semipermeable membrane to separate the DOM from the water. Ion exchange is a process that uses a resin to exchange ions with the DOM.

There are a number of research needs related to color in water. These needs include the development of more effective and cost-effective treatment technologies, the identification of the health effects of color in drinking water, and the development of methods for predicting the formation of disinfection byproducts.

There are a number of regulatory challenges associated with color in water. These challenges include the lack of a federal drinking water standard for color, the variability of state and local regulations for color, and the difficulty in enforcing color regulations.