Ricard Devesa

A study of organic compounds that caused a serious taste and odor episode of water supply in two residential areas in Catalonia (N.E. Spain) was carried out. Sweet and paint/solvent odor were the main descriptors used by consumers. Some cases of sickness and nausea were also associated with drinking water consumption by the consumers. Closed-loop stripping analysis (CLSA) combined with sensory gas chromatography and gas chromatography mass spectrometry detection were used to study the problem. As a result, 3-(trifluoromethyl)phenol (CAS number 98-17-9) was for the first time identified as a responsible of an odor incident in drinking water. Concentration levels of this compound were up to 17,000 ng/L in groundwater and up to 600 ng/L in distributed water. Odor threshold in water for 3-(trifluoromethyl)phenol was determined as 13 ng/L (45 °C).

The role of sulfate and nitrate in the taste of drinking water is not entirely clear. Taste threshold concentrations (TTCs) were estimated for these two species by the 3-AFC method by a trained panel, as sodium and calcium salts. In both cases TTCs for nitrate were about 100 mg NO₃/L, twice the usual reference value of international recommendations. TTCs for sulfate were about 160 mg SO₄/L (sodium salt) and 80 mg SO₄/L (calcium); 75% detection values were also estimated for both anions. An experiment with a series of duo-trio tests plus preference showed that sulfate at low concentrations tended to improve the taste of water. However, at high concentrations it was perceived negatively: salty and bitter were the main descriptors used. The reversion concentration took place between 176 and 259 mg SO₄/L. These results indicate that nitrate has to be considered an important issue for health, but with no relevant role in the taste of water. Sulfate shows a positive influence at moderate concentrations but becomes negative at high levels. The usual aesthetic-based level of 250 mg/L established by international regulations appears to be reasonable. The findings of this study with trained panellists are preliminary. Future research with consumer panels is recommended.

The drinking water supply in the Barcelona region has recently experienced a radical change because three new facilities with membrane technology have come into service (i.e. reverse osmosis and electrodialysis reversal in the Llobregat river and a sea water reverse osmosis desalination plant. The aim of the study was to predict the reaction of consumers to changes when blends between desalinated and conventionally treated sources were supplied. Seven blended samples of membrane and conventionally treated waters and three unblended water samples were assessed using ranking, scoring and triangle tests. Trained and untrained panels were used for taste assessment. The number of available tasters for each session was 13–14 trained tasters and between 22 and 32 volunteers. Therefore, the total number of tasters ranged between 36 and 46. Ranking and scoring results from both panels were similar (i.e. no significant difference in an independent t-Test), even though the trained panel displayed a better sensitivity in the triangle test. Water preference scores ranged from 3.6 to 6.5. Multiple comparison procedures (i.e. Fischer’s Least Significant Difference Test) on global normalised liking results allowed us to define a grouping structure for water samples that were significantly different from the others. It was determined that membranes would contribute positively to consumer perception. For the relationship between the salinity represented by the total dissolved solids (TDS) and water preference, the overall trend indicated that water with lower salinity was preferred. These results confirm that the assessment of water is primarily driven by TDS even though other factors (i.e. pH, mineral composition) can play a significant role in the liking of water, which is consistent with previously published reports.

Chlorinous flavors are a leading cause of customers' dissatisfaction with drinking water. Potential differences in chlorine perception were investigated by conducting sensory testing experiments in France and Spain to assess consumers' sensory sensitivity (chlorine flavor detection threshold and supra-threshold intensity) as well as their liking of and acceptability for chlorinated solutions. In both countries, two groups of panelists were constituted based on their water drinking habits (tap vs. bottled water). Chlorine flavor detection threshold was found to vary depending on countries (0.17 mg/L Cl₂ in France and 0.56 mg/L Cl₂ in Spain). Taking into account that mean flavor detection thresholds were found in agreement with chlorine residuals delivered at tap, it is likely that habituation may explain sensitivity differences between countries. This hypothesis is supported by results showing no significant sensitivity difference at detection threshold levels, but significant differences between tap water and bottled water consumers at supra-threshold levels (flavor intensity). In addition, consumers' liking and acceptability for chlorinated water was found to be in agreement with sensitivity: the higher the sensitivity the lower the acceptability for chlorinated waters. Thus, French consumers or bottled water drinkers showed a lower appreciation of chlorinated water solutions and were especially less inclined to accept chlorinated water as drinking water delivered at tap.