This paper attempts to measure the economic benefits of tap water quality improvement using a specific case study of Ulsan, one of the large cities in Korea. To this end, we apply the contingent valuation (CV) method by employing a one-and-one-half bounded spike dichotomous choice question format. We surveyed a randomly selected sample of 400 households in Ulsan and asked respondents questions in person-toperson interviews about how they would willing to pay for the program. Respondents overall accepted the contingent market and were willing to contribute a significant amount (1,611 won), on average, per household per month. This willingness varies according to individual characteristics such as education level and income. The aggregate value of the program in Ulsan amounts to approximately 8 billion won per year.