The aim of this study was to estimate the costs and the health benefits of the following interventions: increasing access to improved water supply and sanitation facilities, increasing access to in house piped water and sewerage connection, and providing household water treatment, in ten WHO sub-regions. The cost-effectiveness of each intervention was assessed in terms of US dollars per disability adjusted life year (DALY) averted. This analysis found that almost all interventions were cost-effective, especially in developing countries with high mortality rates. The estimated cost-effectiveness ratio (CER) varied between US$20 per DALY averted for disinfection at point of use to US$13,000 per DALY averted for improved water and sanitation facilities. While increasing access to piped water supply and sewage connections on plot was the intervention that had the largest health impact across all sub-regions, household water treatment was found to be the most cost-effective intervention. A policy shift to include better household water quality management to complement the continuing expansion of coverage and upgrading of services would appear to be a cost-effective health intervention in many developing countries.