Global dilution factors for domestic wastewater in rivers
(A tool for estimating river concentrations of chemicals originating from domestic sewage effluent)

The river flow was derived from the 0.5 degree resolution annual and monthly composite runoff fields produced by Fekete et al. (http://www.compositerunoff.sr.unh.edu/). These long term average runoff values were estimated across the globe by combining a simple water balance model and observed river discharge data. The monthly and annual runoff are accumulated using a topographically-derived flow direction grid to produce river flows at a 0.5 degree resolution. The domestic wastewater effluent was obtained by combining population estimates and per capita domestic water use estimates (national estimates). Population estimates were based on the GPW (Gridded population of the world) v.3 data set for 2005 at 0.5 degree resolution (http://sedac.ciesin.columbia.edu/data/set/gpw-v3-population-count-future-estimates).

Four main data sources (public domain) for national per capita domestic water use were used:

i) Gleick (2009)

ii) Food and Agriculture Organisation (http://www.fao.org/nr/water/aquastat/main/index.stm)

iii) World Resource Institute

iv) Organisation for Economic Co-operation and Development (http://www.oecd.org/env/indicators-modelling-outlooks/oecdenvironmentaldatacompendium.htm)

Where discrepancies arose in domestic water use data, only the data for the year 2000 or later was retained, and from these the lowest estimate was selected to provide a more conservative value for the DF. These selected national estimates were then used to derive a 0.5 degree resolution grid of domestic water use.