In an earlier study in rural Guatemala, 257 households that received flocculant-disinfectant to treat their drinking water had 39% less diarrhea than 257 control households. Three weeks after completion of the study, national marketing of the flocculant-disinfectant was extended into the study communities. Six months later, we assessed frequency of and characteristics associated with purchase and use of the flocculant-disinfectant by revisiting the original study households and administering a questionnaire. Four hundred sixty-two households (90%) completed the follow-up survey; 22 households (5%) purchased the flocculant-disinfectant within the preceding 2 weeks and used it within the last week. Neither being randomized to the intervention group during the efficacy study nor combined spending on laundry soap, toothpaste, and hand soap in the preceding week was associated with active repeat use. Even after efficacy was demonstrated within their community and an aggressive sophisticated marketing approach, few households purchased flocculant-disinfectant for point-of-use water treatment.