Lowtech Graph lists low-tech options for every need of a home. Here you can compare them, find tutorials to build them, and link them together into a circular system. Why low-tech?
Keeping the water from the shower, the sinks and the washing machine apart from what leaves the toilet. Nothing downstream can reuse greywater unless it was separated here, so this is the decision the rest of the greywater options depend on, and it is far cheaper to do while the pipes are being laid.