There is a well-established body of literature on monetary valuation of water ecosystem services to support the case for sustaining tropical forests. However, this literature is heterogeneous in its purposes and approaches and has not been carefully compared, providing a fragmented view of the values of forest water services. This paper addresses this knowledge gap through an orderly review and a regression meta-analysis of existing valuation studies at the regional level in South and Central America. This analysis allows identifying some factors that systematically influence forest values. However, it also reveals a lack of a systematized approach to valuation and a lack of sufficiently coherent evidence. This represents a barrier for the incorporation of the values of water ecosystem services into decision-making.