Significant pressures have been identified for waterbodies that are At Risk of not meeting their water quality objectives under the Water Framework Directive. While there are a multitude of pressures in every waterbody, the significant pressures are those pressures which need to be addressed in order to improve water quality. Many of our waterbodies have multiple significant pressures. A robust scientific assessment process has been carried out to determine which pressures are the significant pressures. This has incorporated over 140 datasets, a suite of modelling tools, and local knowledge from field and enforcement staff from the Local Authorities, Inland Fisheries Ireland and EPA. Impacts from domestic waste water include nutrient and organic pollution. This assessment synthesises over a decade of field studies on on-site systems in Ireland across many different soil types and combines factors relating to the efficiency of the septic tank systems with attenuation factors for the hydrogeological flow pathway.