This is an in-depth analysis by the Foundation for the Economics of Sustainability (Feasta) on the desirability of separating wastewater nutrients at the source -- that is, at the toilet -- rather than mixing them together with greywater and processing them into sludge. The report was prepared in 2015 for the Irish Environmental Network, and as such some of its analysis is specific to Ireland, but most of the conclusions are applicable to the US and elsewhere.