“…Non-probability samples are commonly used in public opinion research to make population estimates and in this case was the best way to reach the population of interest: high water users. Although there are limitations in being able to generalize non-probability samples, they have been shown to yield results as good as, or even better than, probabilitybased samples (Abate, 2008;Twyman, 2008;Vavreck & Rivers, 2008). The researchers fully acknowledge the limitations of opt-in panels and the lack of coverage associated with on-line survey designs.…”