Combustion-synthesized titanium carbide ceramics uniformly disperse silver, producing silver ions and hydroxyl radicals in water. This generates antimicrobial activity against various bacteria. One such bacterium is Streptococcus mutans, a gram-positive anaerobic bacterium known as a major pathogen of dental caries. In this study, we analyzed the inhibition of oral biofilms and S. mutans by ceramic water in in vitro and human studies. S. mutans strains showed significantly lower antimicrobial and sucrose-dependent adhesion activity in the presence of ceramic powder compared with untreated culture medium. Confocal microscopy revealed that S. mutans biofilm structures with ceramic powder were thin and coarse. Twenty-seven volunteers (13 males, 14 females; 18-37 years old, mean 25.2 years) were enrolled for subsequent studies. After each meal, one group was asked to rinse with ceramic water while the other rinsed with untreated water for 1 week. After 1 week, the rinsing contents were switched between the groups and the same protocol was followed for an additional week. After rinsing with ceramic water, the average plaque score was 43.0 ± 3.7, which was significantly lower than the baseline value (74.1 ± 5.7, p < 0.001). However, no significant difference was observed when rinsing with untreated water. In addition, the total number of S. mutans in saliva was significantly reduced after rinsing with ceramic water compared with untreated water (p < 0.05). These results suggest that ceramic water possesses antimicrobial activity against S. mutans and inhibits biofilm formation. Rinsing with ceramic water can also inhibit dental plaque formation and S. mutans colonization in humans.