Greywater System Sizing Calculator
Enter your household size, shower and laundry habits, and local water cost to find out how much greywater you produce, what system capacity you need, and how fast it pays for itself. Nothing uploaded.
Household habits
Reuse & cost
Reuse goal
Learn more: Greywater systems and household savings
How greywater volume is calculated and what water sources can be reused
Greywater is wastewater from showers, baths, and washing machines - it excludes toilet water (blackwater). A typical shower uses 20-25 gallons, and a laundry load uses 25-40 gallons depending on machine size and age. The calculator multiplies household size by showers per person per week and laundry loads per week, then divides by 7 to get daily gallons. For example: 4 people x 5 showers/week x 20 gal/shower + 6 laundry loads/week x 25 gal = 500+150 = 650 gallons per week, or ~93 gallons per day. Only greywater suitable for irrigation or toilet flushing should be reused. Greywater with grease (kitchen sink) or contamination should go to sewer unless the system filters it specially.
System capacity sizing and realistic payback timelines
Greywater systems must hold enough to serve peak demand. A 1.5x daily volume buffer is recommended: if your home generates 100 gallons daily, you need a 150-gallon reservoir to handle shower surges and laundry cycles. Payback depends heavily on local water costs - USD 2-3 per 1,000 gallons in water-abundant regions takes 8-10 years, while areas paying USD 8-12 per 1,000 gallons see payback in 2-4 years. Labor, permits, and connection to landscaping or toilet supply also affect total installation cost. Most systems save USD 100-300 annually; check your utility bill for your actual rate before sizing. Greywater also reduces municipal water treatment load and helps during droughts, adding non-financial benefits.
FAQ
How much greywater does a typical household produce?
A family of 4 showering 5 times per person weekly generates roughly 400 gallons per week from showers alone, plus another 150-200 from laundry loads. That's 80-120 gallons per day in total greywater. The calculator estimates based on your household size, shower frequency, and laundry habits, then recommends a system capacity of 1.5x daily volume to handle peak usage.
What greywater sources are safe to recycle?
Shower and bathtub water are the cleanest greywater sources, suitable for both irrigation and toilet flushing. Washing machine water works for irrigation but is riskier for toilets due to soap residue. Avoid kitchen sink greywater unless using an advanced system with grease trap and filtration. Never mix in toilet water (blackwater). Always check your local code - some jurisdictions prohibit greywater reuse entirely, while others require permits and specific system designs.
How long until the system pays for itself?
Payback depends on your water and sewer rate (check your utility bill), system cost, and water usage. A USD 1,500-2,000 system in an area with USD 8-10 per 1,000-gallon rates typically pays back in 3-6 years. In low-cost water regions (USD 2-3 per 1,000 gal), payback stretches to 10+ years. Rebates and tax incentives in some jurisdictions can reduce upfront cost significantly.