Quantifying the impact of septic tank systems on eutrophication risk in rural headwaters

► First direct UK evidence that nutrient emissions from septic tank systems affect water quality in rural areas. ► Septic tank soakaways on impermeable soils failed to adeqautely treat the septic tank effluent. ► The downstream eutrophication impact of septic tank systems largely depends on stream discharge volumes. ► Septic tank systems act as mini-point sources and need to better managed in catchment management planning.