Greywater Loop

Greywater — water from showers, sinks, and laundry, but not toilets — represents roughly 60% of household water use. It carries soap residue, skin cells, and food particles, with lower pathogen loads than blackwater but still requiring treatment before reuse. With proper handling, it is suitable for subsurface irrigation and toilet flushing.

The loop sits in the building section like this: drain lines from the shower, bathroom sink, and washing machine converge in the basement or crawlspace, dropping into a small surge tank (50–100 liters) that buffers peak flows. From there, a gravity line or small pump routes water to the garden — not sprayed on leaves, but released into mulch basins around fruit trees, shrubs, and perennials. Alternatively, the water rises to a header tank that gravity-feeds toilet cisterns on the floors below. The plants that thrive on greywater are those tolerant of mild alkalinity from soap: comfrey, rhubarb, fruit trees, native shrubs. Avoid root vegetables and leafy greens where greywater contacts the edible part. In jurisdictions permitting greywater reuse — California, Arizona, most of Australia — the systems are simple and legal. The critical detail: separate the plumbing at rough-in, even if the loop isn't installed immediately. Pre-plumbing costs almost nothing; retrofit later costs thousands.