subject: 1. Saving water by re-using graywater efficiently in the garden [print this page] 1. Saving water by re-using graywater efficiently in the garden
This aritcle is an excerpt of our Graywater Guide: from Buckets to Irrigation Systems.
With over 60 pages of detailed information, you can learn everything you need to know before deciding what is the best way for you to save water & money. The download is free and does not require registration.
In the U.S., many websites recommend saving graywater by connecting a hose to the washing machine outlet, and having this water run into a series of mulch basins in the garden (the generally accepted maximum number of mulch basins is 10).
While this feels good, it isn't saving as much water as you may think.
As an example, consider re-using the graywater in a hot and dry location such as Tucson, Arizona.
If you put 5 gallons of water in one 4 foot diameter mulch basin every day (150 gallons per month), you have not saved 5 gallons per day
In Tucson, Arizona, that basin only needs 12 gallons for the whole of July for low to medium water-use plants & trees
The actual amount saved is 12 gallons.
The irrigation efficiency is 12/150 or 8%. The rest of the water simply drained into the subsoil, wasted.
Instead, the 5 gallons per day could be irrigating 90 square feet of garden
A family of four, easily generating 100 gallons of graywater per day, could be irrigating 1,700 square feet in Tucson
The same family could be irrigating over 2,400 square feet in San Diego, just by re-using their graywater.
In my next article, I will explain how graywater can be easily irrigated over such a large area, with or without pumps, and in a safe way approved in U.S. states that have graywater regulations.
Before even considering re-using graywater, you should ask yourself why?
The most common reasons are:
Water shortages - how can I keep my garden alive?
High utility costs - expensive watering the garden
Reducing the load on your septic system - saving money
Going green - attempting to live a sustainable life
If you don't have a garden, re-using graywater within the house requires a treatment system. This doesn't stack up economically if you are connected to a water supply that is relatively inexpensive.
In a non-serviced area it can make sense. Or perhaps you want / need to achieve a certain LEEDs level.
Untreated graywater irrigation systems are now very affordable and make economic sense, but you must establish the context in which it is installed.
If you don't have a garden, or it is extremely low water use, you probably don't need to re-use graywater.
Save water instead by installing low flow shower heads and toilets. Consider a high efficiency washing machine (although from a green perspective the carbon footprint of a new-fangled washing machine is considerably higher than the older style machines).
If you DO have a garden, think carefully about your total water usage.
The following is a great comparison showing how a "whole of property" approach should be considered:
Two people live in a San Diego house on a 7,000 square foot lot. They both have 7 minute daily showers and use the washing machine 4 times each week.
Their garden requires an average of 5,000 gallons per month for 9 months of the year.
Case 1: Using older style shower heads and washing machine, their total annual shower, laundry and garden consumption is 80,950 gallons per year.
Let's imagine rebates were offered for a new washing machine (20 gallons per wash), and free replacement shower heads (2 gallons per minute flow), but they continue to water their garden.
Their annual consumption drops down to 59,380 gallons, a saving of 21,570 gallons.
Case 2: Let's leave everything in place as it was (old shower heads / washing machine), but install an automatic graywater irrigation system, that is 90% efficient.
Their annual consumption drops to 35,950 gallons per year, saving 45,000 gallons per year.
How can that make sense?
Irrigating every day using graywater dripperlines is far more efficient than watering by sprinkler, hose, or reticulation system.
3,000 gallons of graywater per month will achieve a better result for the garden than 5,000 gallons per month of potable water.
I've raised this concept of water context very early in this series of articles because it was a very important issue in Australia. People were changing their shower heads / washing machines, but still irrigating the old way.
In most cases it is cheaper and more beneficial to re-use your graywater outside than to reduce your inside home water use.
Even in new homes, it is about the same cost (or less) to install a graywater irrigation system than a potable water irrigation system, although a make-up water connection may be required if you don't generate quite enough graywater with low flow amenities.
Decide how sustainable you want to be.
You may only have enough graywater to support the plants and trees in the garden beds, and not the lawn.
Maybe you only have enough to water half of your garden, in which case make-up water could be used, or you decide to irrigate selected areas only.
Water conservation is all about knowing what your property needs, and applying only that amount. Don't be tempted to run dual irrigation systems - it invariably results in overwatering. In any of the warmer states, outdoor use exceeds indoor use. Much of the problem is caused by automatic reticulation, using sprinkler heads (very inefficient) with rain sensors, rather than moisture sensors.
This aritcle is an excerpt of our Graywater Guide: from Buckets to Irrigation Systems.
With over 60 pages of detailed information, you can learn everything you need to know before deciding what is the best way for you to save water & money. The download is free and does not require registration.
