Diarrhea is an endemic disease in Indonesia and potentially becoming an outbreak. This study aims to describe the relationship between knowledge, attitudes, and practice of heads of households on water processing and prevalence of diarrhea. A cross-sectional survey was applied to 93 heads of households using simple random sampling technique located in Lampulo village, Kuta Alam sub-district, Banda Aceh, Aceh Province in December 2016. Knowledge, attitudes, and practice on water processing and diarrhea prevalence were assessed using questionnaires. Chi-square test was used to analyze a relationship between water source and prevalence of diarrhea. To see a relationship between knowledge, attitude, and practice of heads of households and diarrhea prevalence used Spearman's coefficient correlation (CI = 95 %; α = 0.05). Results showed that water source and prevalence of diarrhea had no statistical relationship (p = 1.000). From 93 households, 32 (34.4 %) were ever experienced diarrhea and they were used piped water 30 (32.26 %) and well water 2 (2.15 %) as their sources of drinking water. Relationship of knowledge and diarrhea prevalence has low positive correlation (r = 0.219, p = 0.035); attitude and diarrhea prevalence has weak positive correlation (r = 0.326, p = 0.01), practice and diarrhea prevalence has weak negative correlation (r = –0.256, p = 0.013). Knowledge, attitudes, and practice on water processing of the heads of households were correlated to the prevalence of diarrhea. <br>