The Source Apportionment-GIS (SAGIS) Tool quantifies the loads of pollutants to surface waters in the UK from 12 point and diffuse sources, including wastewater treatment works discharges, intermittent discharges from sewerage and runoff, agriculture, soil erosion, mine water drainage, septic tanks and industrial inputs (UKWIR project WW02).

The Source Apportionment-GIS (SAGIS) modelling framework was developed through UWKIR research project WW02: Chemical Source Apportionment under the WFD (UKWIR, 2012) with support from the Environment Agency.

The primary objective of this research was to develop a common modelling framework as the basis for deriving robust estimates of pollution source contributions that would be used to support both water company business plans and the EA River Basin Planning process.

Loads are converted to concentrations in river waters using the SIMulation of CATchments (SIMCAT) water quality model, which is incorporated within SAGIS, so that the contribution to in-stream concentrations from individual sources can be quantified.

Diffuse sources of nutrient pollution are incorporated into SAGIS from the Phosphorus and Sediment Yield Characterisation In Catchments (PSYCHIC) model (developed by a consortium of academic and government organisations led by ADAS Water Quality).

The SAGIS report and tool are available to purchase from UKWIR (£600 + fees for additional data licencing), but is also made available to water companies and the Environment Agency have made some outputs available through the CaBA Data Package.