|In this study, we aimed to estimate value of water quality improvement in terms of bloom-forming algae case. Evaluation subjects were chosen as general public who had an experience on the tap water usage. This study set up six price categories, which are 5,000, 10,000, 20,000, 30,000, 40,000 and 50,000 Korean won (KRW), through preliminary inquiries and then conducted nationwide surveys aimed at major cities. From those investigations, a total of 1,745 samples were used to conduct the empirical analyses. Main results on applying double-bounded dichotomous choice of contingent valuation method (CVM) are as follows. First, the high social class recognized by the general public, postive attitude toward environmental protection, and high level of understanding about sewage treatment process were statistically significant to willingness to pay (WTP) in support of waterbloom removal. On the other hand, the people who experienced contaminated tap water, have a negative attitude toward environmental protection, or believe that current water costs are expensive, did not favor national project so that WTP was on the lower level. Economic benefit by water quality improvement indicates roughly 590 billion KRW.