Most recently, a paper about monitoring urban water sustainability published in the "Journal of Environmental Management" argued that sustainable development is being reconsidered as a process with unknown endpoint. The paper explains that outputs of sustainable urban water systems defined as ‘policies, projects, laws, technologies, and consumption and reuse amounts associated with urban water sustainability goals’ are therefore being viewed as inadequate monitoring instruments. The article proposes a new methodology for sustainability monitoring whereby normality of a system is diagnosed through normality of its supporting inputs in lieu of normality of its complex outputs. Supporting inputs are ‘intents and behaviors that support system goals’. Supporting inputs follow a principle of self-organization to remain in the norm and behavior zone commonly associated with system goals. This implies that normality of supporting inputs can be inferred from their longitudinally normal or Gaussian distribution that can be explored by significance tests. The article identifies fourteen supporting inputs of sustainable urban water systems - such as internet searches, community campaigns, staff training, agent-principal reporting and legislation propositions about water sustainability – and defines quantitative indicators for them. The Shapiro-Wilk test and Kolmogorov-Smirnov test (K–S) of these indicators and a subsequent Boxplot outlying examination of non-normal indicators are undertaken in a case study. Qualitative examination of non-normal supporting inputs confirms the ability of this statistical methodology to detect problems in the system.