Estimate how many gallons of greywater you can capture and reuse from showers, laundry, and sinks for irrigation and toilet flushing.
Greywater is gently used water from showers, bathtubs, bathroom sinks, and clothes washers that can be captured and reused for landscape irrigation or toilet flushing. It does not include water from toilets, kitchen sinks, or dishwashers. Reusing greywater can reduce your freshwater consumption by 30–50%, cutting both your water bill and the strain on local water supplies.
This calculator estimates your daily greywater production from each source, applies a capture efficiency factor (since not all greywater is practically collected), and shows how much can be diverted for reuse. The result helps you size a greywater system, estimate irrigation capacity, and calculate the return on your investment.
Greywater systems range from simple laundry-to-landscape setups costing under $200 to full whole-house systems with filtration costing $2,000–$5,000. Regardless of complexity, knowing your greywater volume is the essential first step in planning.
Tracking this metric consistently enables energy professionals and facility managers to identify consumption trends and implement efficiency improvements before costs escalate unnecessarily.
Greywater reuse reduces potable water demand by 30–50% with minimal treatment. This calculator quantifies your potential, helping you size a system correctly and estimate water bill savings. Precise quantification supports regulatory compliance and sustainability reporting, ensuring that energy data meets the standards required by auditors and industry certification bodies. Data-driven tracking enables proactive energy management, helping organizations reduce operational costs while progressing toward environmental sustainability goals and carbon reduction targets.
Reusable Greywater (gal/day) = Σ(source_gallons) × capture_efficiency_%
Result: 76.5 gal/day
Total greywater sources = 50 + 30 + 10 = 90 gal/day. At 85% capture efficiency, reusable volume = 90 × 0.85 = 76.5 gal/day, or about 27,923 gallons per year.
The simplest system is laundry-to-landscape, which redirects washing machine water directly to garden beds through a diverter valve. More complex systems collect shower and sink water, filter it, and distribute it through drip irrigation. Full systems with storage tanks and pumps can serve both irrigation and toilet flushing.
Your greywater production must align with your irrigation demand. In summer, you may produce less greywater than your garden needs. In winter, you may produce more than plants can absorb. Proper system design accounts for these seasonal imbalances.
A basic laundry-to-landscape diverter costs $100–$200 and can save 15,000+ gallons per year. At $5/1,000 gallons, that's $75/year in water savings alone, paying for itself in 1–2 years. More elaborate systems have longer payback periods but greater total savings.
Greywater includes water from showers, bathtubs, bathroom sinks, and clothes washers. It does not include water from toilets (blackwater), kitchen sinks, or dishwashers due to higher contamination levels.
Yes, when used properly. Greywater should be applied below the surface or under mulch, not sprayed on edible plant parts. Use biodegradable soap and avoid greywater on root vegetables eaten raw.
Greywater can offset 30–50% of total household water use by replacing potable water for irrigation. In arid climates with expensive water, savings can be substantial — $200–$500+ per year.
Capture efficiency accounts for practical losses — not all water reaches the collection point, some is lost in pipes, and some sources may be excluded. 80–90% is a realistic capture rate.
It depends on your jurisdiction. California allows simple laundry-to-landscape systems without a permit. Other states may require permits, especially for systems with storage tanks or indoor reuse.
Yes, but it requires filtration and sometimes disinfection. Toilet flushing reuse systems are more complex and expensive than irrigation-only systems but are common in commercial buildings.