In this article we show how to size an Aqualoop greywater recycling system, whether it is a single family sized application or larger residential system including apartments, condominiums, dorms, and other buildings people live in. There are other greywater sources which we will cover in another article. These include hotels, car washes, large laundries, health clubs, and many others all of which also are great applications for the Aqualoop greywater recycling system.
What is Greywater Recycling and Why Use it?
Before I launch into the design discussion I always feel it necessary to explain what the definition of greywater is and why one may need to recycle the stuff. Greywater as we define it is water that comes from:
- Showers (the biggest source!) and baths
- Bathroom sinks or lavatories
There may be other greywater sources in your particular building, but the ones above pretty much cover it. Greywater can be used technically for any end use depending on treatment regimen. Typically, greywater is treated to various levels adequate for reuse in non-potable uses like toilet flushing and laundry indoors or irrigation and cooling tower make up outdoors. The treatment regimen is critical to determining the range of application even for these non-potable uses.
Greywater recycling is a viable way to manage water due to evolving technologies like Aqualoop and the need to rethink 20th century water supply and management philosophies. With aquifer and surface water depletion from ever increasing demand, we can no longer assume unlimited water supply from nature. On the other side, we have an ever increasing load on our crumbling water treatment infrastructure. Greywater recycling helps reduce demand for municipal water from wells and reservoirs and also reduces the load on large scale wastewater treatment plants.
An Aqualoop greywater treatment system can reduce outside household water demand by over 40%, which is a huge number. Combined with rainwater collection, use of municipal or well water can be eliminated altogether in many cases.
How Much Greywater is There:
Our estimate shows there may be around 33 gallons of greywater generated per person per day on average in a typical residence. This is between about 40% and 70% of total water demand for indoor use. We assume standard low flow fixtures and a reasonable amount of conservation and awareness. The actual amount of greywater generated will of course vary for specific situations. Some people take longer and more frequent showers than others. Some are actually at home more than others. Here is a table listing out our standard assumptions:
Greywater Supply Sources & Assumptions
|Greywater Supply Sources||Measure|
|Showertime Average (mins)||8|
|Bathroom Sink Use PPPD (GPM)||3|
|Total Shower Flow||0.33|
|Total Sink Use (GPD)||25|
|Total Laundry Use (GPD)||4.95|
|Total Water Supply (GPD)||33|
We assume people shower on average for 8 minutes. Some poeple may shower for a low as 4 minutes and some may be in there for 20 minutes. 8 Minutes seems like a good average to us, but use what you believe to be correct. Regardless, since none of your shower water will be wasted, showering will be twice the fun!
We assume a standard low flow shower head of 2.5 GPM although there are many new and high quality heads on the market delivering 1.5-2 GPM. Some shower heads flow far more than 2.5 GPM.
Further assume that a person may take a second shower every few days or may take a long lingering one on the weekend or take a bath which uses more water.
The bottom line is that showers (or baths) make up around 75% of greywater supply and is this the most important to capture!
We assume 3 gallons per day from this source which is around 10% of the total. If capture of this water is problematic, it may not be worth capturing.
We assume a person will run a couple loads of laundry a week. If they have a water smart newer model, each load may use around 15 gallons. As with showers, this number may vary quite a bit.
The greywater sources add up to around 12,000 gallons per person per year or 48,000 gallons for the proverbial family of 4. An apartment building with say 200 units and 300 residents can generate over 3 million gallons per year. This is a serious amount of water and can far exceed what can be captured by rainwater collection in dry regions.
The next thing to know is how this water can be used.
Treated Greywater Uses:
Unlike many other greywater technologies which do coarse filtration only, the Aqualoop process meets NSF 350 water quality standards and is thus suitable for use indoors and can be stored for extended periods. With BOD below 5 PPM and coliforms below 2 CFU, the water can be used for any non-potable application including spray irrigation, toilet flushing, laundry, and cooling tower make up (for commercial scale buildings)
The 12,000 gallons each person generates per year may be used for:
We assume 5 flushes per day with a standard 1.6 gpf toilet. There are many new lower flow models at 1 GPM which do not require double flushes and there may be some ancient commodes out there which use more than 1.6 GPF. Adjust this assumption as you see fit. The annual demand using my assumption is around 3,000 gallons or 25% of the total available.
It is quite easy to use treated Aqualoop water for the cold water in laundry. Using for hot water as well may require a dedicated water heater. Since cold water makes up about 2/3 of the laundry water, this use is worth about 1100 gallons per year.
Typically, irrigation will use any water that is available. This can be done easily by simply sending excess treated greywater to your rainwater tank. You do have a rainwater tank don’t you??!! In our example, there would be around 7900 gallons available for this or 66% of what’s available.
Other uses may include vehicle washing, cooling tower make up, and various process waters. With a little extra treatment, aqualoop treated would be suitable for human contact in showers although local regulations may not have caught up with this concept. See our other blog post which shows that fresh water consumtion can be reduced as low as 5-8 gallons per person per day using these techniques and how rainwater could meet that demand even with rainfall as low as 12″ per year!.
The Bottom Line:
We figure Aqualoop greywater recycling can reduce household municipal or well water consumption by over 40%. This goes a long way toward being water independent and alleviating water stress in drought stricken areas. This can translate into hundreds and in some places thousands of dollars saved on water bills over the course of a year. In fact in places like Atlanta, or Seattle, or San Francisco, ROI’s can beat the stock market for Aqualoop in single family homes!
For commercial scale, the ROI’s are always much much higher due to economies of scale. It is not unusual to see ROI above 80% with payback in less than 5 years.
Thanks for reading. As always please let us know what you think and any questions or challenge points you may have.