How Much Water Can a Greywater System Really Save?
Mason LogueA greywater system does not make your household use less water. It takes water you have already used, in the shower and the washing machine, and sends it out to the landscape instead of down the sewer. What it saves is the potable water you would otherwise have sprayed on your garden. That distinction shapes every number on this page, so we want it stated before the arithmetic starts.
For a typical single-family home, showers and laundry alone put about 50 gallons a day down the drain, roughly 18,250 gallons a year. Add baths and bathroom sinks and a full capture system in a family of four handles around 30,000 gallons a year. Below we show where those figures come from, what they mean for your household size, and where the honest limits are.
What a household actually produces
The best current measurements of American household water use come from the Water Research Foundation's Residential End Uses of Water study, now in its third version. It logged fixture-level events with smart meters rather than asking people to guess. Two numbers matter most here.
- Showers: 12.55 gallons per event, at about 3.0 shower events per household per day.
- Clothes washer: 24.55 gallons per load, at about 0.48 loads per household per day.
Multiply those out and you get a shade under 50 gallons of shower and laundry greywater per household per day, about 18,250 gallons a year, before you route a single other fixture into the system.
Per person, showers, baths and the clothes washer together come to about 16.6 gallons per person per day. Bringing bathroom sinks in raises that to roughly 21 gallons per person per day. For scale, total indoor use runs about 38.5 gallons per person per day, so a full capture greywater system is working with a little over half of everything that comes through the meter and into the house.
Annual capture by household size
The table below uses 21 gallons per person per day, which assumes showers, baths, laundry and bathroom sinks are all plumbed to the system. Capture only the laundry and you would divide these figures by roughly four.
Source Water Research Foundation, Residential End Uses of Water, Version 3 (2026), REUWS 3 educational dataset, WRF project 5242. Per-capita figures for showers, baths, clothes washers and bathroom sinks, extended to annual totals by Water Wise Group.
| People in the home | Gallons per day | Gallons per year |
|---|---|---|
| 1 | 21 | About 7,700 |
| 2 | 42 | About 15,300 |
| 3 | 63 | About 23,000 |
| 4 | 84 | About 30,700 |
| 5 | 105 | About 38,300 |
| 6 | 126 | About 46,000 |
About the 40,000 gallon figure
You will see 40,000 gallons a year on greywater marketing, including some of our own older material, and we would rather explain it than let it sit there unqualified. Full capture in a real home runs 25,000 to 40,000 gallons a year. A family of four lands near 30,000. Reaching 40,000 and above takes five or more people, or older fixtures that use more per event than the current averages. Forty thousand is the top of the range, not the middle of it, and a two-person household with modern low-flow showerheads should plan on something closer to 15,000.
Where the saving actually comes from
Worth being precise about the mechanism, because it is the part most articles get wrong. Diverting shower and laundry water does not reduce your indoor use. That water has already run through the fixture. What it does is stop you buying city water for the garden. Every gallon the system delivers to your landscape is a gallon of treated, metered, paid-for water you no longer purchase, right through the growing season.
The practical consequence is simple. The saving is only as large as the irrigation it replaces. A household with a quarter acre of planting in Phoenix will use every gallon the system produces and want more. A household that irrigates almost nothing, or one in a wet climate with six months of rain, will see the saving approach zero for much of the year. Before you buy, look at what you currently spend on outdoor watering. That number, not the capture figure, is your ceiling.
The same logic applies in reverse during drought. When outdoor watering is restricted or priced steeply, the value of every diverted gallon rises, which is why systems pay back fastest in dry regions. We go through that case in detail in our guide to greywater during drought and water restrictions.
What this does to your bill
It lowers it, and the reason is straightforward. Through the growing season your landscape is drinking water you paid the utility for. A greywater system replaces that supply with water you have already bought once. Those gallons come off your meter, so they come off the volume charge on your bill.
The saving is usually bigger per gallon than your average rate suggests. Most utilities price water in tiers, and outdoor irrigation is exactly what pushes a household from the cheap base tier into the expensive upper ones. The gallons a greywater system displaces tend to be the most costly water you buy all year. In a summer-peaking district that effect alone can be worth more than the raw volume implies.
Two parts of the bill will not move, and we would rather you know that up front than be surprised. Most utilities calculate your sewer charge from winter water use rather than metering what actually leaves the house, so summer irrigation savings usually leave the sewer line unchanged. The fixed monthly service charge does not move either. The saving lands on the water volume charge, which in an irrigating household through summer is the line that matters.
To size it for your own home, pull a summer bill and a winter bill. The difference between them is roughly what you are spending on outdoor watering. Find your per-thousand-gallon rate and your tier thresholds, then multiply against the capture figure for your household size from the table above. For the other half of the calculation, see what a greywater system costs.
Which system for which household
Aqua2use GWDD
The Aqua2use GWDD suits most single-family homes. It takes water from laundry, showers and bathroom sinks, runs it through four stages of progressively finer filtration, and pumps it out to subsurface irrigation. For a household of two to four, that means capturing somewhere between 15,000 and 30,000 gallons a year, depending on how many fixtures you route into it.
Aqua2use Pro
The Aqua2use Pro is built for larger homes, schools and small commercial sites where the peak flow is higher and the run to the irrigation zone is longer. Its rated flow is 25 gallons per minute at 16 feet of head, with a maximum of 47 gallons per minute at 3.3 feet of head. Those two conditions belong together. A pump figure quoted without the head it was measured at tells you nothing useful, because flow falls as the height and distance the pump has to push against increase. Size against the head your actual installation imposes, not against the maximum.
What owners say
Dave in Baja, Desert Region
“We live in the desert, and water is scarce… It’s been great to have all this additional water available for the garden.”
Dave set up separate sewer lines for greywater and black water, using buried irrigation lines to keep his garden thriving despite minimal rainfall.
Mike Ellsworth, Tiny House Owner
“While planning our tiny house, this system seamlessly integrated into our wastewater plan. The county had no questions. We’re extremely satisfied.”
Even with minimal plumbing space, Mike’s Aqua2use system ensures every drop counts.
Richard, Arizona
“The unit is attached to our laundry discharge and sends water out through hoses to water the yard, with great results.”
Richard's GWDD keeps a yard green on water that used to leave the property.
Working out your own number
The table above is a starting point. To get closer to your own situation:
- List the fixtures you can realistically plumb into a system. Laundry is usually the easiest, showers next, bathroom sinks last.
- Count events rather than minutes. Showers at 12.5 gallons each, laundry loads at 24.5 gallons each, are better estimates than a guess at gallons per minute.
- Multiply the daily total by 365 for annual capture.
- Compare that against your actual outdoor watering. The smaller of the two numbers is what you will really save.
One older figure worth retiring while you do this: the widely repeated 25 gallons for a ten minute shower. Measured shower events average 12.55 gallons, roughly half that, because most showers are shorter than ten minutes and most showerheads are now well under 2.5 gallons per minute. Building your estimate on the old number will roughly double your expected saving and leave you disappointed.
Where that leaves you
A greywater system in an ordinary American home moves 15,000 to 40,000 gallons a year from the sewer to the landscape, with 30,000 a fair planning figure for a family of four. That water is free once the system is installed, and it displaces potable water you would otherwise buy at your utility's rates, which in a dry climate with tiered pricing is the most expensive water you purchase all year. Your water bill falls accordingly through the watering season. What it will not do is lower your indoor consumption or shrink a fixed service charge. Judge it on the irrigation it replaces, and the numbers hold up.
