In her 2010 book, The Just City, Susan Fainstein evaluates justice in her case-study cities (Amsterdam, New York and London) though a three dimensional analysis of justice (Equity, Diversity and Democracy). Her approach, popular among Western scholars, cannot be replicated as such in disadvantaged cities such as Bujumbura because of the important processes happening outside the formal institutional and policy frameworks. The main claim of this article is that justice cannot be evaluated in such contexts without taking into consideration the informal. Through a multi-scalar analysis of informality in household water provision in Bujumbura, the article assesses the importance of informality on the different dimensions of Fainstein’s Just City concept. Informality has to be included in the considerations if the concept of the ‘Just City’ is used as the analytical lens through which to make policy recommendations. This analytical lens then enables us to evaluate justice in - and rethink the governance of - urban systems with high degrees of informality, such as that of household water provision in Bujumbura.