The uncertainty of input parameter data, taken from the scientific literature, is rarely discerned. We assume that as data uncertainty increases, model output uncertainty also increases, with the potential for major impacts on decision making and policy. We examined reported nitrogen (N), phosphorus (P) and sediment losses from various land uses to determine the uncertainty of these data. Land uses considered included agriculture, forestry, and urban. When information was available, we attempted to stratify land use by management practice (particularly for agriculture). A number of uncertainty calculations were used, including uncertainty from Root Mean Square Error and Mean Absolute Error. For those data with the largest uncertainty, we examined sensitivity of the APEX and SWAT models by normal range and differential sensitivity analysis using a range for each input indicated by its uncertainty. We report uncertainty for N, P and sediment in water from three land uses and the sensitivity of two models to these input parameters. This type of analysis and its ramifications should be made available to all decision makers using model output information.