Greywater from sinks, showers, and laundry is directed to an interior botanical treatment cell: a constructed planter built into the interior of the building, typically along the south wall within the greenhouse space. The botanical cell is a sealed, lined container filled with a sequence of filter media — typically gravel of decreasing particle size from bottom to top, with a growing medium at the surface — that provides both mechanical filtration and a substrate for a diverse community of microorganisms that biologically process the organic matter and nutrients in the greywater.

Plants growing in the botanical cell absorb processed nutrients, take up water through their roots, and transpire moisture that contributes to the humidity of the greenhouse interior. The planters can be designed to grow productive food plants — bananas, papayas, herbs, and other warm-climate species thrive in interior botanical cells — turning the waste treatment system into a food production asset. The treated water that accumulates at the bottom of the cell is pumped to flush the building’s toilets, completing the first stage of the water cycle.

Interior Botanical Cell: Key Design Parameters

• Minimum cell volume: 100–150 liters per person in the household

• Filter media layers: coarse gravel (bottom) → medium gravel → fine gravel → growing medium (top)

• Inlet: greywater enters at the top of the cell and percolates downward

• Outlet: treated water collected at bottom, pumped for toilet flushing

• Overflow: gravity overflow to conventional leach field (code-required backup)

• Plant selection: moisture-tolerant productive species; no root crops