This report has evaluated existing methods applied in a number of related fields for quantifying and reducing uncertainty in models that may be applied in Urban Water Systems. Numerical models may be applied to address one of the key aims of the PREPARED project, and aid in optimising the use of existing water supply and sanitation systems. However, such modelling approaches must consider inherent system uncertainty, which is reviewed in Section 2 of this report; uncertainty of both aleatory and epistemic nature affects UWS modelling in both Water Distribution Networks and Urban Waste Water Systems .