This paper has developed and estimated a valuation model for water quality improvement. After reviewing more than 100 studies, we set up a data set that has 332 valuations from 38 distinct studies. Based on the data set, we estimate a linear valuation model, which can then be used to predict the mean willingness to pay by households living in a given region for water quality improvement at a given site. For instance, the willingness to pay by a typical household living in the state of Iowa for a water quality increase from 40 to 50 (out of 100) at a one-square-mile aquatic site, like Iowa's Spirit Lake, is predicted to be $137.52. The valuation model developed in this paper is particularly convenient when we want to evaluate the benefit of a project that aims at improving water quality, but a primary study is too costly or time consuming.