1. Check the governing rule
Ask the local health, plumbing, building, wastewater or environmental authority which sources, uses, treatment, storage, setbacks, permits and qualified trades apply. Regional examples are not global permission.
2. Define the source
List showers, baths, bathroom basins and clothes washers separately. Do not include toilets. Kitchen and utility sources are treated differently across jurisdictions and may have higher fats, solids, chemical and pathogen concerns.
3. Measure real volume
Measure fixture flow and typical duration, appliance water per cycle and weekly frequency. Keep short event volume separate from the daily average because receiving basins must accept the event when it happens.
4. Define one allowed end use
State the hydrozone, plant types, soil, slope, exposure controls and seasonal need. Keep edible-crop, surface discharge, spray, indoor reuse and toilet-flushing questions with the local authority and validated treatment requirements.
5. Match supply to demand
Use local reference evapotranspiration, effective rainfall, plant factor, area and irrigation efficiency. Plan a diversion destination when supply exceeds demand or when soil is saturated, frozen or not actively growing.
6. Distribute each event
Use whole outlets or branched paths that produce a defensible volume per receiving basin. Check pipe routing, air entry, cleanouts, appliance requirements and access without creating a potable cross-connection.
7. Check receiving capacity
Use field infiltration evidence and realistic basin void volume. Stop and redesign if water surfaces, ponds, runs off, reaches structures or approaches prohibited wells, property lines or water bodies.
8. Preserve diversion and labeling
Keep the original sewer or septic path available where required. Clearly identify non-potable components and make maintenance positions understandable to future occupants.
9. Commission by observation
Run one source at a time, confirm every outlet, watch a complete event, check the receiving area later, and record actual volumes. Correct weak or overloaded branches before normal use.
10. Maintain the system
Inspect filters, diverters, valves, outlets, mulch or subsurface emitters and signs of odor, surfacing or plant stress. Update the plan when occupants, appliances, soaps, plants or climate change.
Worked example
A household measures 180 L/day of potentially reusable water but its peak hydrozone needs only 140 L/day. The plan sizes outlets for the washing-machine event, verifies basin acceptance, and keeps at least 40 L/day plus wet-weather supply on an approved diversion path rather than forcing reuse.
Sources
- San Francisco Public Utilities Commission — Graywater Design Manual
- Washington State Department of Health — Greywater Reuse
- U.S. EPA WaterSense — Water Budget Tool
- Australian Government — Australian Guidelines for Water Recycling