How convincing are mainstream economists in the public debate? Can they mitigate the impact of “populist” messages? We study these questions in relation to the ownership of water management companies, a topic that has been targeted by left-wing populism in Chile, Italy, Paris, Berlin, Spain among other places. Private and foreign ownership are seen with reluctance by many people, associated with the perception that water is a special good and resource. By contrast, the position of mainstream economists is that whether ownership is public or private is not important, given that companies are properly regulated. We present the results from an online experiment in which we compare the impact of three communication treatments on opinions about water ownership. Treatment 1: an “agnostic” text on the reality of water ownership and regulation in Spain. Treatment 2: similar information as in 1 plus arguments taken from “sophisticated left-wing populists.” Treatment 3: similar information and arguments as in 1 & 2 plus arguments typical of expert mainstream economists. The length of the three texts is kept constant. We have 1050 participant, representative of the Spanish population. They are paid 6 euros (5 if they do not answer well a control question about what they read). The online questionnaire was administered by a specialized company. The participant pool was randomly split in 3 subsamples of 350 each. The participants in the three subsamples are asked to answer the same questionnaire elicitating their opinion on public vs private ownership, but have to read partially different texts (treatments 1, 2, or 3) in the middle of the questionnaire. We find that the Spanish citizens in our participant pool have on average moderate opinions about public or private ownership, according to our questionnaire, with a high degree of diversity. Populist arguments are convincing when they are not counter-argued by experts. The arguments of expert economists were more convincing than we expected and effective at mitigating (and even eliminating) the influence of populist arguments.