A cluster, randomized control trial was conducted to assess the effects of social marketing approach on purchase rates and water treatment behavior of Klorfasil, a chlorine-based household water treatment product among seven villages in Thomassique, Haiti, from May to December 2016. Villages were randomized to the free-trial (257 households) or cost-sharing (240 households) group. Households in the free-trial group were allowed 30 days of free Klorfasil use before purchase decision. Households who purchased Klorfasil were then followed up for 30, 60, and 180 days. At the last follow-up, respondents were asked if they would like to repurchase Klorfasil. Questionnaire survey and water quality assessment by residual-free chlorine were conducted in each survey. Chi-square test, t-test, and logistic regression were applied. The first purchase rate of the cost-sharing group was significantly higher than that of the free-trial group (79.2% versus 67.3%). By contrast, the repurchase rate of the free-trial group was higher (82.9% versus 66.3%). However, the overall repurchase rate was 71.6% and the proportion of long-term users was significantly higher in the cost-sharing group (56% versus 47%). Water treatment rates in the cost-sharing group were significantly higher than those in the free-trial group in the first and final surveys (odds ratio [OR] = 0.15, OR = 0.32). Households with high and medium economic status both had significantly higher purchase rates than low economic status households (OR = 4.40, OR = 1.94). Households with higher educated respondents had significantly better water treatment practices (OR = 2.15). The free-trial approach did not increase the first purchase rate but increased the repurchase rate later. The cost-sharing approach significantly encouraged long-term usage.