While not required to establish a likelihood of confusion, “[a] showing of actual confusion would of course be highly probative, if not conclusive, of a high likelihood of confusion.” In re Majestic Distilling Co., 315 F.3d 1311, 1317 (Fed. Cir. 2003). But this depends on the nature and extent of any actual confusion. For example, a single instrance of actual confusion could be deemed de minimus and not entitled to significant weight. But a single instance of actual confusion could be bolstered by accompanying testimony suggesting that it was not an isolated instance, and could be “illustrative of how and why confusion is likely” in that it shows that the consumer became confused as to the source of the parties' goods based on the marks. See Molenaar, Inc. v. Happy Toys Inc., Opp. No. 91054350, 1975 TTAB LEXIS 1, at *5-6 (TTAB 1975) (“The record shows at least a single instance of actual confusion, albeit there is testimony which indicates that there have been more instances of actual confusion. While a single instance is insufficient as evidence from which to conclude that applicant's mark has consistently caused confusion, the single instance of confusion is at least ‘illustrative of a situation showing how and why confusion is likely'.”) (quoting Libbey-Owens-Ford Glass Co. v. Thermoproof Glass Co., 390 F.2d 770, 771 (CCPA 1968)). 

In Zero Techs., LLC v. Hangzhou Yilin Tech. Research Co., Ltd., Cancellation No. 92081980 (TTAB July 14, 2025), the Board granted a petition for cancellation of a registration for the mark ZEROLIQUID for “water filtration units” after finding confusion likely with the registered mark ZEROWATER for “water filtering units for household use.” 

The goods were found to be in-part legally identical. See Cai v. Diamond Hong, Inc., 901 F.3d 1367, 1372 (Fed. Cir. 2018) (citing In re Viterra Inc., 671 F.3d 1358, 1362 (Fed. Cir. 2012) (“[I]t is well established that, absent restrictions in the application and registration, [identical] goods and services are presumed to travel in the same channels of trade to the same class of purchasers.”) (internal quotation marks omitted)). This weighed heavily in favor of a likelihood of confusion.

Although "zero" was found to have a suggestive meaning when used in connection with water filtering goods, and thus "highly suggestive" of the goods and only entitled to a narrower scope of protection, the marks nonetheless were "very similar" which weighed heavily in favor of likelihood of confusion. 

Notably, evidence of a single instance of actual confusion, accompanied with testimony that this was not an isolated occurence (e.g., “We have received numerous complaints from owners of ZEROWATER®-branded pitchers regarding the lesser quality of ZEROLIQUID-branded replacement filters that they purchased believing were manufactured and sold by us but in fact were manufactured and sold by Respondent.”), was found to have lent "some support" for the conclusion that confusion was likely. 

TTABlog's comment about relying on one incident of confusion: "Gimmeabreak!"