Why Reuse Greywater?
Greywater refers to lightly used water from showers, bathroom sinks, and laundry machines. It excludes toilet waste but still contains soaps and detergents. Instead of sending this water down the drain, many households redirect it for irrigation or toilet flushing. Doing so reduces freshwater demand and lowers utility bills. This calculator estimates how much water and money you can save annually and whether the investment in a greywater system pays off over its lifespan.
Input Assumptions
The daily greywater volume depends on household size and habits. The average shower uses about 65 liters, while a load of laundry consumes around 50 liters. Summing contributions from each source provides an estimate. The reuse percentage represents how much of that volume can be captured and safely applied. Not all greywater is reusable—some may be too hot, too contaminated, or produced when irrigation isn't needed. A conservative reuse rate is 50%.
Water Cost and Savings
Utilities charge for both water supply and wastewater treatment. Many regions bill by the cubic meter (1,000 liters). If your rate is $2.50 per m³, reusing 100 liters per day saves dollars annually, before maintenance costs. The calculator multiplies daily volume by reuse percentage and 365 to determine annual reuse volume, then divides by 1000 to convert to cubic meters and multiplies by the water price.
Installation and Maintenance
Greywater systems range from simple manual buckets to automated filtration and distribution networks. Installation costs can vary from a few hundred dollars for DIY kits to several thousand for professionally plumbed setups that integrate with existing irrigation. Annual maintenance includes filter replacement, pump electricity, and occasional inspections. These expenses are subtracted from savings when computing net benefit.
Payback Period
The payback period indicates how many years it takes for cumulative savings to equal the installation cost. Mathematically, , where is installation cost and is annual net savings (water savings minus maintenance). A shorter payback suggests a more financially attractive project. However, some homeowners pursue greywater recycling for environmental reasons even if payback exceeds the system's lifespan.
Example Calculation
Consider a family that generates 200 liters of greywater daily and can reuse 60% for landscape irrigation. At $3.00 per m³, annual water savings equal:
dollars.
If installation costs $1,500 and maintenance is $50 per year, net savings are $81.40 and payback is roughly 18.4 years. Over a 25‑year lifespan the total benefit becomes $2,035, meaning the system eventually saves more than it costs, especially if water prices rise.
Environmental Impact
Every liter of water reused reduces demand on reservoirs and the energy required for pumping and treatment. Multiply annual reuse volume by your region's energy intensity to estimate electricity saved. Some municipalities offer rebates for greywater systems, further improving financial return.
Quality and Safety
Greywater should not touch edible plant parts or be stored for more than 24 hours because bacteria can proliferate. Use biodegradable soaps and avoid chlorine bleach. Filtering hair and lint before irrigation prevents clogged emitters. The calculator assumes compliance with local codes; always check regulations before installing a system.
Landscape and Legal Considerations
Local building codes dictate how greywater may be used. Some jurisdictions allow only subsurface drip systems to prevent human contact, while others require treatment units if water is stored. Understanding permits and inspection requirements avoids fines and ensures public health. Homeowners associations may have additional rules regarding visible piping or irrigation methods.
System Types
Greywater setups range from simple laundry-to-landscape hoses to complex systems with settling tanks, pumps, and sand filters. "Laundry-to-landscape" uses a diverter valve on the washing machine drain hose to route water directly to mulch basins around trees. More elaborate designs collect shower and sink water into holding tanks, where debris settles before pumping to drip lines. Choosing the right configuration depends on budget, yard layout, and willingness to maintain filters.
Plant Selection
Not all plants tolerate soaps or high sodium content. Salt-sensitive species like azaleas or blueberries may suffer if irrigated with greywater from detergent-heavy sources. Hardy ornamentals, fruit trees, and lawn grasses generally thrive. Rotating irrigation zones prevents buildup of salts in soil, and occasional freshwater flushing keeps root zones balanced.
Maintenance Tips
Every system benefits from routine checks. Inspect filters monthly, clean lint traps, and monitor distribution lines for clogs. Winterizing in cold climates may involve draining exterior pipes to prevent freezing. Tracking system performance in a journal helps identify patterns, such as reduced flow indicating a blocked filter.
Case Study
A suburban household in Arizona installed a $2,000 greywater system that redirected shower and laundry water to xeriscape gardens. With a reuse volume of 150 liters per day, they saved over $120 annually on water bills and reduced municipal demand during drought restrictions. By selecting drought-tolerant plants and using biodegradable soaps, they maintained a vibrant landscape while demonstrating how small-scale greywater reuse contributes to regional conservation efforts.
Limitations
This tool provides a high‑level estimate. Actual savings depend on seasonal irrigation needs, system efficiency, and changes in water pricing. Rainy climates may reuse less greywater outdoors, whereas arid regions may use nearly all of it. For a full feasibility study, consult a professional who can analyze site‑specific factors.
Conclusion
Greywater recycling transforms waste into a resource, lowering utility bills and easing pressure on freshwater supplies. By combining your household's water habits with cost parameters, this calculator offers insight into potential savings and payback period. Use it as a starting point to evaluate whether a greywater system fits your sustainability goals.