You don't need biased subjects to have ambiguous results. Suppose for instance all people from group A can taste chlorine at 20ppm, and below that threshold, th

You don't need biased subjects to have ambiguous results. Suppose for instance all people from group A can taste chlorine at 20ppm, and below that threshold, those individuals have no perceived chlorine taste. Individuals from group B can taste chlorine only at 80ppm and above. If the tap water has chlorine starting at 100ppm and the filter removed half (as stated in the article) then we would have water at 100ppm and 50ppm. Some observers would perceive a difference and some would not. If the Pur filter removed 90% of chlorine, then individuals in both groups would perceive a difference in taste. To point, this experiment depends on your taste preferences, as the author has stated that there is a physical difference in the makeup of the water samples after filtration.