The dataset captures the temporal and spatial variability of dilution factors (DFs) around the world using geographically referenced data sets at 0.5 degree resolution and includes long term annual and monthly DFs grids. The dilution factor (DF) dataset is composed of 13 rasters: 1 annual and 12 monthly. DFs are a critical component in estimating concentrations of 'down-the-drain' chemicals which enter freshwaters following consumer use via the domestic waste water stream (e.g., pharmaceuticals, household cleaning products). The DF is defined as the ratio between flow and total domestic wastewater effluent generated within a catchment. The methodology was specifically developed to be applied across the world even within those countries where river flow data and/or wastewater effluent data is scarce. The present dataset has potential for a wide international community (including decision makers and pharmaceutical companies) to assess relative exposure to 'down-the-drain' chemicals released by human pollution in rivers and, thus, target areas of potentially high risk.