Consumers assess their tap water primarily by its taste, odor, and appearance. Starting in 1979, USEPA promulgated Secondary Maximum Contaminant Levels (SMCLs) as guidance for contaminants with organoleptic effects and also to maintain consumers’ confidence in tap water. This review assesses the basis for the 15 SMCLs (aluminum, chloride, color, copper, corrosivity, fluoride, foaming agents, iron, manganese, odor, pH, silver, sulfate, total dissolved solids, zinc) and summarizes advances in scientific knowledge since their promulgation. SMCLs for aluminum, color, pH, silver, sulfate, total dissolved solids, and zinc are appropriate at current values and remain consistent with sensory science literature. Recent advances in sensory and health sciences indicate that SMCLs for chloride, copper, fluoride, iron, and manganese are too high to minimize organoleptic effects. The SMCLs for corrosivity and foaming agents may be outdated. The SMCL for odor requires rethinking as the test does not correlate with consumer complaints. Since current stresses on source and treated waters include chemical spills, algal blooms, and increased salinization, organoleptic episodes that negatively impact consumer confidence and perception of tap water still occur and may increase. Thus, adherence to SMCLs can help maintain production of palatable water along with consumers’ confidence in their water providers.

Surprisingly few quantitative studies have addressed the question of whether visually impaired individuals evidence, perhaps in compensation for their loss of vision, increased acuteness in their other senses. In this experiment we sought to determine whether blind subjects outperform sighted subjects on a number of basic tests of chemosensory function. Over 50 blind and 75 sighted subjects were administered the following olfactory and gustatory tests: the University of Pennsylvania Smell Identification Test (UPSIT); a 16-item odor discrimination test; and a suprathreshold taste test in which measures of taste-quality identification and ratings ofthe perceived intensity and pleasantness of sucrose, citric acid, sodium chloride, and caffeine were obtained. In addition, 39 blind subjects and 77 sighted subjects were administered a single staircase phenyl ethyl alcohol (PEA) odor detection threshold test. Twenty-three of the sighted subjects were employed by the Philadelphia Water Department and trained to serve on its water quality evaluation panel. The primary findings of the study were that (a) the blind subjects did not outperform sighted subjects on any test of chemosensory function and (b) the trained subjects significantly outperformed the other two groups on the odor detection, odor discrimination, and taste identification tests, and nearly outperformed the blind subjects on the UPSIT. The citric acid concentrations received larger pleasantness ratings from the trained panel members than from the blind subjects, whose ratings did not differ significantly from those of the untrained sighted subjects. Overall, the data imply that blindness, per se, has little influence on chemosensory function and add further support to the notion that specialized training enhances performance on a number of chemosensory tasks.

More than 100 years of research has focused on removing acute and chronic health threats to produce safe drinking water, but limited research has focused the consequences of removing minerals that affect drinking water taste and health. This paper covers the human sense of taste, typical variations in drinking water taste, comparisons of global taste standards, the role of water chemistry and future research needs for understanding consumer preference. Results of several consumer tap and bottled water acceptability investigations conducted by the authors are presented.

Overall, in the air pollution control field, odor concentration and intensity as well as hedonic rating have been well studied to the point where some level of standardization is being developed or is already in place. However, there has been no standardization with respect to odor quality characterization. There is now sufficient understanding of the types of odorous compounds that can arise from wastewater treatment processes to develop an odor classification scheme. This article presents the first wastewater odor wheel or classification scheme that should form the foundation for the evolution of odor quality data reporting with links to chemical causes.

The content of anions and cations (as minerals) in tap water can positively and negatively affect taste. Undesirable tap water taste can arise from levels of anions and cations above or below regulatory limits, from minerals without regulatory limits, and from a lack of minerals in water. However, no thorough investigation of the interactions of the human sense of taste, drinking water quality, and water treatment has been conducted. Tap water taste has, historically, not caught the attention of the drinking water industry at large. However, it is becoming an important issue because water treatment techniques such as reverse osmosis are gaining more applicability and can strongly influence tap water taste. Therefore, drinking water practitioners, designers, and regulators need to better understand how water quality and water treatment can affect the taste of water.

Traditional research has focused on the visible effects of corrosion--failures, leaks, and financial debits--and often overlooked the more hidden health and aesthetic aspects. Clearly, corrosion of copper pipe can lead to levels of copper in the drinking water that exceed health guidelines and cause bitter or metallic tasting water. Because water will continue to be conveyed to consumers worldwide through metal pipes, the water industry has to consider both the effects of water quality on corrosion and the effects of corrosion on water quality. Integrating four key factors--chemical/biological causes, economics, health and aesthetics--is critical for managing the distribution system to produce safe water that consumers will use with confidence. As technological developments improve copper pipes to minimize scaling and corrosion, it is essential to consider the health and aesthetic effects on an equal plane with chemical/biological causes and economics to produce water that is acceptable for public consumption.

Two episodes of unacceptable tastes and odors, which corresponded with levels of geosmin in the water that were much higher than the background level of 20 ng/L or less, occurred in Philadelphia during 1985. The source of one episode was found to be a localized bed of algae in the Schuylkill River. An existing taste‐ and odor‐control program, which utilizes instrumental and sensory analyses, was largely responsible for the effective management of the episodes. Hydraulic strategies were used to reduce the treatment plant's intake of geosmin, and powdered activated carbon in the treatment train further reduced the geosmin level. Dilution of this treated water with other finished waters in the distribution system also diminished the impact of geosmin on the taste and odor of Philadelphia's water.

Since 1981, when the use of free chlorine was curtailed to control trihalomethanes at the Baxter Treatment Plant in Philadelphia, Pa., a seasonal cucumber flavor problem occurred. Flavor profile analysis was the only tool available to guide treatment. During 1990, the cucumber odor was tracked more than 250 mi (402 km) up the Delaware River to the Cannonsville Reservoir, and the odor‐causing compound was identified as trans,2‐cis, 6‐nonadienal. Algae growth beneath the winter ice produced the compound. Other treatment plants on the river that used free chlorine for disinfection and a final residual never had a problem with trans,2‐cis,6‐nonadienal. Therefore, use of chlorine was increased at the Baxter plant to control the cucumber flavor. Studies were conducted on trans,2‐cis, 6‐nonadienal to describe its sensory characteristics and analytical detection limit.