Greywater explained: what it is, what it is not, and how to reuse it simply

Greywater is water already used once in showers, sinks and the washer. It is not blackwater (toilet and kitchen water, which carries organic matter and goes to the drain, no debate) and it is not clean water either: it is the one in between, and there is a lot of it. In a typical home, 50 to 70% of the water that enters leaves as grey.

The golden rule: use it fast, never store it

Greywater does not keep beyond 24 hours: soap plus warmth turns it into a culture broth. Every sensible reuse spends it the same day, on applications that do not touch people: toilets, drip irrigation of ornamentals at soil level (never sprinklers), patio cleaning.

The reuse ladder, from zero pesos to real plumbing

• Level 0, free: bucket in the shower... though if you are collecting the cold-water wait, the real problem is better solved by a hydro-return that sends it back to the heater clean instead of degrading it to grey.
• Level 1, ~200 pesos: washer discharge hose to the yard or to a bucket for the toilet. 60 to 100 liters per load. Use low-sodium biodegradable soap if it goes to plants.
• Level 2, ~1,500 pesos: a three-way valve on the washer discharge: lever to 'garden' or 'drain' per load. The best cost-benefit in home reuse.
• Level 3, a project: dual piping with a solids trap and filter feeding toilets and irrigation. Justified in new builds or remodels; in an existing house, level 2 gives 80% of the benefit at 10% of the cost.

Mistakes that ruin the experiment

• Watering leafy vegetables with greywater: no. Ornamentals and trees: yes.
• Sprinklers: they turn greywater into aerosol you breathe. Always water at the base.
• Chlorine and fabric softener in plant-bound water: it burns them. Switch soap or send that load to the drain.
• Storing it 'for the drought': at 48 hours it smells like the reason you should not.

The right order of investment

First stop generating waste (the hot-water wait, leaks, an efficient showerhead), then reuse what remains. Not dirtying a liter is cheaper than treating it: that is why reuse is step two of the 20-measure plan, not step one.

If you are also considering rain harvesting, the systems complement each other and the harvesting guide explains when each one makes sense.