Diarrhoeal diseases are associated with high morbidity and mortality, especially in children less than five years of age in many low- and middle-income countries (LMICs). This cross-sectional convergence mixed-method study explored water, sanitation and hygiene challenges as the important contributors to childhood diarrhoea in rural Tanzania. The study involved questionnaire survey (N=340), key informant interviews (KII) (n=10) and eight focus group discussions (FDG) (n=61). Prevalence of diarrhoea was 22.2% and 18.7% in Sanza and Iwondo Wards, of Manyoni and Mpwapwa Districts respectively. Improved houses (iron roof and baked brick walls) were more common in Sanza, while 80% of the houses in both wards had earth floor. Water sources in dry period and frequency of sharing water sources with animal were significantly different between wards (P<.001). Boiling drinking water was uncommon, practised by only 5.2% and 8.6% of the households in Sanza and Iwondo, respectively. More than 95% of the households in both wards used traditional pit latrines, and latrine sharing was more common in Iwondo than in Sanza (P=.035). The themes from KII and FGD were: knowledge of occurrence and causes of diarrhoea, water safety, hand-washing, availability of improved sanitation services, keeping chickens inside the house overnight, health effects associated with keeping chickens inside the house and knowledge of occurrence and causes of diarrhoea. Mixed methods analysis through merging data sets revealed poor community knowledge on the causes of childhood diarrhoea, ineffective hand washing, seasonal variation of drinking water sources and high human-chicken interactions. Prevention and control of gastrointestinal infections in resource-poor settings should promote the use of cheap and locally available resources and feasible practices in response to the existing challenges related to water and sanitation services, financial constraints, economic activities, and cultural practices.