Previous chapters of this guide have discussed how much water is required by plants, and where the water is needed (top 3″ – 6″ of soil).
The graywater diversion methods discussed in this chapter all apply the graywater to the soil in different ways, significantly affecting the irrigation efficiency.
These are the commonly accepted methods of reusing untreated graywater:
- Branched Drain (or similar)
- Laundry to Landscape
- Gravity Dripperline
- Pumped Dripperline
Before going into the pro’s and con’s of each method, the concept of how much water is actually saved needs to be understood.
If you put 10 gallons of water in one 4′ hole in the ground every day, you have not saved 10 gallons per day.
In Tucson, Arizona, that hole only needs 12 gallons for the whole of July for medium water use plants.
If this was done daily, then 300 gallons has been irrigated over the month, instead of the required 12 gallons.
The actual amount saved is 12 gallons. The irrigation efficiency is 12/300 or 4%.
This may sound extreme, but I have seen quite a few branch drain systems set up this way (the rest of the water goes down into the subsoil and is wasted, unless trapped by clay in which case the roots of the plants may rot).
So while on the surface some methods may appear to be very inexpensive for the amount of water diverted, the amount of water actually saved needs to be reviewed.