Sustainability is a major issue in the WASH sector and financial sustainability in particular needs more attention. We need to find better ways of covering the recurrent costs of water and sanitation, particularly in reaching the poorest and most vulnerable in society. Innovative approaches to financing, including recent ideas such as development impact bonds and municipal bonds, are to be welcomed. However, we must also exercise caution and not value novelty over outcome. One recent example is the rise of water projects funded by the carbon market. This article highlights some of the key risks and potential pitfalls of such schemes. The aim is not to target any single developer or scheme, but to highlight the key issues so that they can be addressed and everyone can have confidence in the impact of these activities – avoiding reputational issues and accusations of ‘greenwashing’.