Background. Water, sanitation, and hygiene (WASH) are immediate priorities for human survival and dignity in emergencies. In 2010, > 90% of Syrians had access to improved drinking water. In 2011, armed conflict began and currently 12 million people need WASH services. We analyzed data collected in southern Syria to identify effective WASH response activities for this context. Methods. Cross-sectional household surveys were conducted in 2016 and 2017 in 17 sub-districts of two governorates in opposition controlled southern Syria. During the survey, household water was tested for free chlorine residual (FCR). Descriptive statistics were calculated, and mixed effect logistic regressions were completed to determine associations between demographic and WASH variables with outcomes of FCR > 0.1 mg/L in household water and reported diarrhea in children < 5 years old. Results. In 2016 and 2017, 1281 and 1360 surveys were conducted. Piped water as the main water source declined from 22.0% to 15.3% over this time. Households accessed 50–60 l per capita daily (primarily from private water trucking networks). Households spent ~ 20% of income on water and reported market-available hygiene items were unaffordable. FCR > 0.1 mg/L increased from 4.1% to 27.9% over this time, with Water Safety Plan (WSP) programming strongly associated with FCR (mOR: 24.16; 95% CI: 5.93–98.5). The proportion of households with childhood diarrhea declined from 32.8% to 20.4% over this time; sanitation and hygiene access were protective against childhood diarrhea. Conclusions. The private sector has effectively replaced decaying infrastructure in Syria, although at high cost and uncertain quality. Allowing market forces to manage WASH services and quantity, and targeting emergency response activities on increasing affordability with well-targeted subsidies and improving water quality and regulation via WSPs can be an effective, scalable, and cost-effective strategy to guarantee water and sanitation access in protracted emergencies with local markets.