Contaminant of the Month: Drinking water aesthetics

What are water’s aesthetic factors?

• The aesthetic aspects of drinking water include: taste, odor, color, turbidity, salinity, hardness, softness and temperature.
• The aesthetics are generally not health-related. However, consumers can easily detect them, so they can have significant effects on perceptions of water quality and acceptability.
• These attributes are the source of most complaints to water suppliers and frequently lead consumers to choose home treatment or bottled water.

Taste & odor

• Taste and odor detection are intermixed in human senses and are closely related.
• Some substances can be detected at low concentrations, and detection varies by individual and other factors such as water temperature.
• Some tastes, such as certain minerals, are desirable, but they also vary by personal preference and experience.
• Other tastes, such as high salinity, are undesirable at sufficient levels. Organics, such as geosmin, 2-methylisoborneol and chlorophenols, are detectable at micrograms or nanograms per liter.
• Chemical tastes, such as gasoline, indicate potentially significant contamination.
• Chlorine and chloramine tastes are frequent causes for consumer dissatisfaction and often lead consumers to choose home treatment or bottled water.
• Metallic tastes, such as iron, can be caused by iron in source water or pipe corrosion because of pH effects.
• Sulfides and their rotten-egg odors are caused by sulfate-reducing bacteria in the aquifer.

Color

• Natural sources or corrosion can cause metallic colors. For instance, color can be metallic from iron, copper or organic-like humus.

Turbidity

• Turbidity or cloudiness is caused by suspended particulates that diffuse light. The condition becomes noticeable in a glass at about 4 nephalometric units (ntu). The particulates could be innocuous if they are caused by calcium carbonate precipitation, but turbidity can be an indicator of inadequate filtration and disinfection, overdosing of aluminum coagulants, or sloughing of biofilms from pipes.

Salinity

• Salts in the water are usually sodium chloride or similar salts. The recommended concentration is below 500 milligrams per liter, but many water supplies in some areas exceed that level.

Hardness & softness

• Water hardness is caused by divalent ions, primarily calcium and magnesium, but barium or strontium could factor in as well.
• Excessive hardness causes scale formation and soap precipitation.
• Excessively soft water is difficult to rinse completely and can also corrode pipes.

Treatment techniques

• Taste and odor: Use carbon treatment and possibly oxidation with chlorine, chlorine dioxide or ozone if it is caused by organics. A simple activated carbon filter can easily remove chlorine taste, while air or chlorine oxidation removes sulfide taste and odor. For metallic tastes, first determine the cause and suitable treatment.
• Color: Activated carbon treats organic color. Inorganic color requires identification of the cause and suitable treatment.
• Turbidity: Filtration can remove turbidity after determining the cause.
• Salinity: Reverse osmosis is the usual treatment for excess salinity.
• Hardness: Cation exchange is the common home treatment choice, but municipal plants use lime softening.
• Softness: Calcite filters and likely pH adjustment can harden water.

Regulation

• Federal secondary drinking water regulations exist for most aesthetic factors, but they are not mandatory. States have the option to include them in their drinking water standards.

Conclusion

• Even though aesthetic components do not usually have direct public health significance, they are important in public satisfaction and perception of drinking water quality as well as in decisions about using tap water versus bottled water or home treatment. They could also indicate more significant water contamination, so understanding the causes and determining appropriate corrective actions are important. Public water suppliers that do not pay sufficient attention to consumer perceptions do so at their peril.

Dr. Joe Cotruvo is president of Joseph Cotruvo and Associates, LLC, Water, Environment and Public Health Consultants. He is a former director of the EPA Drinking Water Standards Division.