Though controversial, water fluoridation has been hailed as one of the top-ten public-health achievements of the 20th century in the United States of America. In this article, we aim to investigate the public sense of water fluoridation as reflected on Twitter, using data from 2009 to 2017. To this end, tweets related to water fluoridation were collected using queries such as "fluoridated water or fluoride water," "water fluoridation or fluoridation of water," and hashtags related to water fluoridation. The collected tweets ( = 218,748) were examined through informetric, linguistic (word sentiment, word frequency, and word network analyses), and issue tweet analyses. We found that Twitter users who tweeted about water fluoridation in English between 2009 and 2017 constituted about <0.01% of all users including non-English users. In their tweets, words such as "poison" and "waste" were the strong negative sentiment words most often used. Of the top 30 words most frequently used, words related to information sources on water fluoridation and the safety of water fluoridation appeared more often than words related to its efficacy. Additionally, the words related to information sources on water fluoridation and the safety of water fluoridation were found to be core terms in the sentences of tweet mentions. Our linguistic analyses indicate that Twitter users responded sensitively to words that emphasize negative aspects of fluoridation. This is clearly shown in our issue tweet analysis, where tweet mentions expressing negative opinions about water fluoridation accounted for at least 59.2% of all mentions. By contrast, <15% of tweet mentions were found to be positive. These findings suggest that professionals need to reevaluate the current state of online information about water fluoridation, and improve it in a way so that the public can easily access reliable information sources.