A randomized controlled trial of four interventions was conducted using tubewells (n=2,486), liquid sodium hypochlorite (‘Clorin’) distributed with an improved water vessel (n=2,305), hygiene promotion (n=1,877), and a combination of the three (n=2,040) to create an evidence-base for water policy in Afghanistan. A fifth group served as a control (n=2,377). Interventions were randomized across 32 villages in Wardak province. Outcomes were measured through two household surveys separated by one year and twice-weekly household surveillance conducted over 16 months. The households receiving all three interventions showed reduction in diarrhoea compared with the control group, through both longitudinal surveillance data (IRR [95% CI]=0.61 [0.47–0.81]) and cross-sectional survey data (AOR [95% CI]=0.53 [0.30–0.93]). This reduction was significant when all household members were included, but did not reach significance when only children under five were considered. These results suggest multi-barrier methods are necessary where there are many opportunities for water contamination. Surveillance data suggested a greater impact of interventions on reducing diarrhoeal diseases than data from the surveys. Higher economic status as measured through household assets was associated with lower rates of diarrhoea and greater intervention uptake, excepting Clorin. Use of soap was also associated with lower prevalence of diarrhoea.