Dec. 31, 2011: As of August of this year, the use of greywater is now legal and approved (by permit) for residential irrigation use. Let’s first take a look at what greywater is, how it can be used and how pragmatic it is to do so.
.jpg)
Greywater (or gray water) is all the water that has been used in your house, EXCEPT the toilet. Toilet water is blackwater, which requires extensive pre-treatment and is not approved for residential irrigation use. Greywater is the water used in your kitchen and bathroom sinks, showers, bathtubs and laundry room (provided you don’t wash diapers in it). It is collected and diverted from your sanitary pipes before it mixes with blackwater . It comprises about 50-80% of household water usage. The “average” household uses 127,000 gallons of water a year in total domestic use (not irrigation).That water nows goes down the sewer or into the septic tank and there.gif)
are further costs associated with that to dispose of it. Wouldn’t it be great if we could use that water beneficially to irrigate our landscape? Wouldn’t it? Well maybe, we’ll see. All that glitters, may not be grey.
Oregon greywater code stipulates that greywater can only be used for “beneficial purposes”. That means you just can’t dump it outside your house. It’s got to be directed to a useful purpose, like irrigating plants. The code has 3 different permitting levels:
Type I – For residences that generate less than 300 GPD (gallons per day). The water cannot be stored more than 24 hours and can only be applied through sub-surface (below the ground) irrigation.
Type II – For any structure that generates less than 1200 GPD. The water can be store longer than 24 hours but must treated by chemical or biological means to reduce suspended solids and organic matter. It can be applied by drip irrigation on the surface of the soil.
Type III – Anything that doesn’t fall within type I or II permits. This greywater must receive type II treatment and a chemical disinfectant. It can be applied through a sprinkler system.
There is a lot more to the codes than this and I would highly recommend you go to the Oregon DEQ website if you have further interest. http://www.deq.state.or.us/wq/reuse/graywater.htm#Intro
So let’s look at the advantages and disadvantages of greywater. (IMHP – In my humble perspective)
ADVANTAGES:
1.Reduction of some of your freshwater irrigation needs
2.Less strain on sewer or septic systems. Particularly septic systems benefit from less water that has to be handled
3.You feel good by doing something concrete to reduce your water footprint.
DISADVANTAGES:
1.The irrigation water cost you save for the “average” landscape is not huge. The average greywater generation of an average household (and keeping in mind that finding the truly average of anything that’s not a math equation is like finding the Holy Grail) is probably about 100 GPD. At current Portland water rates ($3.09/784 gals) that’s a cost savings of .39/day or about $46.80 over an irrigation season.
Now if you compare that with the cost of installing a greywater system . . . here’s where it’s tricky. Since greywater irrigation is so new and largely untested, few if any contractors have installed these to come up with an average cost. I haven’t. From researching some current on the market residential greywater systems, I estimate about $1500 installed (and I’m probably underbidding) and that would be for a drip system that might cover 50-100 plants. So the payback time on that investment would be 32 years. (Granted that there are other investment returns of environmental and community benefit . . . but I don’t know how to figure those out).
2.To me the biggest disadvantage with the type 1 greywater systems is the inability to store. If you need to irrigate your plants you need to take a shower (preferably a long one) or do your laundry. Frequency and .jpg)
amounts of water are totally dependent on the inside water use. That makes for alot of variability which some plants can take and some plants can’t. From a pragmatic standpoint, greywater irrigation of lawns is out. Irrigating vegetable gardens isn’t that feasible. Fruit trees seem to be the best use for type 1 greywater use.
3.Greywater irrigation systems take a lot of maintenance. Because of suspended solids and fatty residues in the water (kitchen sink water is the worst culprit), filtration systems, pumps, distribution lines and emitters get clogged easily. Often you won’t know when a system is malfunctioning until you see plants dying. The more complicated the greywater system (ie type II or III) the more maintenance and the more components that can malfunction.
4.You can only use your greywater system when plants need irrigation. That means when there’s not enough rainfall. That means in the Pacific NW that it can’t be used for 6-7 months of the year. You have to have a diverter valve that diverts the greywater back to it’s original disposal route.
5.It takes unconventional irrigation components. Greywater piping should be purple pipe. We don’t want to .jpg)
confuse it with white PVC potable water pipe. Conventional drip irrigation clogs easily, so often, the delivery system must be modified so this happens less. For type III irrigation sprinkler use, you must use large impact heads and special dirty water valves. It just takes a whole lot more customizing of the installation.
Note: The greywater technology for commercial irrigation systems (parks, golf courses, etc.) has been around for years and is well established and works, but often these systems use treated effluent from sewage plants. The greywater is treated offsite which makes it quite a bit different from residential, onsite treatment.
6.More complicated systems, like type III, must have disinfection monitoring 3 times a week.
7. Greywater cannot contact any edible portion of a vegetable. That means for vegetable gardening no root crops can be watered by greywater.
In summation and in my humble perspective (as a contractor who has not installed a greywater system and has no hands-on experience), my feelings towards greywater are . . . well , a little gray. But that’s OK, because it matches my life philosophy very well – no blacks or whites, only shades of gray. I think in limited particular situations, it can be a pragmatic and sustainable choice and, in some situations, it is not. I think I’ll try it first in my home lab before installing and warranting a system for a client.
Two years ago I had to replace my septic tank sump pump, which I did myself. I can’t imagine a more unpleasant task and it is my most fervent desire that I am dead or in a retirement home before I need to replace it again. If greywater irrigation will help me meet that goal, I’m willing to try it. I’ll let you know next year, hopefully, how it worked out.
Happy New Year!