Keller, V. D. J.; Williams, R.; Lofthouse, C.; Johnson, A. C.

Global dilution factors for domestic wastewater in rivers

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.

Publication date: 2014-07-11

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Format of the dataset : Esri ASCII GRID

You must cite: Keller, V. D. J.; Williams, R.; Lofthouse, C.; Johnson, A. C. (2014). Global dilution factors for domestic wastewater in rivers. NERC Environmental Information Data Centre.


Dilution factor values along the coastlines must be handled with care due to higher uncertainty in accounting for population discharging to sea rather than rivers.

User should be aware that higher uncertainties arise when estimating river flows and, hence, dilution factors in catchments smaller than 25 000 km2.


Study area
Temporal extent
2013-12-31    to    …

Supplemental information

Other useful information regarding this dataset:

Keller, V.D.J., Williams, R.J., Lofthouse, C. and Johnson, A.C. 2014. Worldwide estimation of river concentrations of any chemical originating from sewage-treatment plants using dilution factors. Environmental Toxicology and Chemistry 33(2), 447-452

Provenance & quality

The river flow was derived from the 0.5° resolution annual and monthly composite runoff fields produced by Fekete et al. ( 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° 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° resolution ( Four main data sources (public domain) for national per capita domestic water use were used: i) Gleick (2009), ii) Food and Agriculture Organisation (, iii) World Resource Institute, iv) Organisation for Economic Co-operation and Development ( 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° resolution grid of domestic water use.

Correspondence/contact details

Dr Virginie Keller
Centre for Ecology & Hydrology
Maclean Building, Benson Lane, Crowmarsh Gifford
OX10 8BB
United Kingdom


Keller, V. D. J.
Centre for Ecology & Hydrology
Williams, R.
Centre for Ecology & Hydrology
Lofthouse, C.
Centre for Ecology & Hydrology
Johnson, A. C.
Centre for Ecology & Hydrology

Other contacts

Environmental Information Data Centre
NERC Environmental Information Data Centre


Spatial representation type
Spatial reference system
WGS 84


Topic categories
Inland Waters
catchment,  Dilution factor,  down-the-drain chemicals,  environmental risk assessment,  exposure,  modelling,  Modelling PEC,  Pollution rivers,  Water quality