Continuous in situ turbidity measurements can be used to estimate real-time TSS (Total Suspended Solids) concentrations in urban water systems. In order to obtain reliable TSS results from continuous in situ turbidity measurements, a set of methods were developed directed to: (i) assess concentrations and associated uncertainties for instantaneous samples applying lab reference methods, (ii) detect samples with low representativeness by means of multivariate outliers analysis, (iii) establish regression functions between TSS and turbidity values that could be used for obtaining real-time concentrations, accounting for uncertainties. Based on the above elements, a methodology for assessing TSS concentrations based on in situ and continuous turbidity measurements was constructed and coded in MatLab®, obtaining a program untitled DROP (Data Relationships Of water Pollutants).