An Introduction to Greywater by zzz22140

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									An Introduction to
Greywater
                         (Part I)
      Reusing this valuable
     resource for irrigation,
        conservation, and
      environmental health.

          By Art Ludwig


A      ny wastewater generated in the
       home, except water from toilets,
         is called greywater. Dish,
shower, sink, and laundry greywater
make up 50 to 80 percent of residential
                                               What to Do With Greywater?

                                                   Conventional plumbing systems
                                               dispose of greywater via septic tanks
                                               or sewers. The many drawbacks of this
                                                                                            uses. This saves money and increases
                                                                                            the effective water supply, especially in
                                                                                            regions where irrigation is needed.
                                                                                                • Less strain on septic tanks or
                                                                                            treatment plants. Greywater, which
“wastewater.” It’s a shame to lose this        practice include overloading treatment       comprises the majority of the waste-
precious resource when greywater can           systems, contaminating natural waters        water stream, contains vastly fewer
be reused for other purposes, espe-            with poorly treated effluent, and a high      pathogens than blackwater and 90
cially landscape irrigation.                   ecological/economic cost.                    percent less nitrogen (a nutrient that
   Toilet-flush water is called blackwa-            Instead, you can reuse this water.       is a problematic water pollutant).
ter. There are a few systems, such as          The most common reuse of greywater           Reducing a septic system’s flow by
branched-drain green septic systems or         is for irrigation. It can also be cascaded   getting greywater out greatly extends
constructed wetlands, that can safely          to toilet flushing or for laundry.            its service life and capacity.
recycle toilet water; they will not be                                                          • More effective purification. Grey-
discussed in the context of this article,      Why Use Greywater?                           water is purified to a spectacularly high
though I do address them in my book,                                                        degree in the upper, most biologically
Create an Oasis with Greywater.                   It is said that there is no such thing    active region of the soil. This protects
   Contaminated or difficult-to-handle          as “waste,” just misplaced resources.        the quality of natural surface and
greywater, such as solids-laden kitchen        Greywater systems turn “wastewater”          groundwaters.
sink water or water used to launder            and its nutrients into useful resources.         • Feasibility for sites unsuitable
diapers, I call “dark greywater,” though       Why irrigate with drinking water when        for a septic tank. For sites with slow
most regulators consider these black-          most plants thrive on used water con-        soil percolation or other problems,
water. However, the level of pathogens         taining small bits of compost?               a greywater system can partially or
in even the darkest greywater is a small          Unlike many ecological stopgap            completely substitute for a costly, over-
fraction of that in blackwater.                measures, greywater use is part of           engineered septic system.
   Wastewater without added solids,            the fundamental solution to many                 • Reduced use of energy and chemi-
such as warm-up water from the hot             ecological problems. The benefits of          cals. This reduction is due to the
water faucet, reverse-osmosis purifier          greywater recycling include:                 reduced amount of freshwater and
drain water, or refrigerator compressor           • Reduced use of freshwater. Grey-        wastewater that needs pumping and
drip, is called clearwater.                    water can replace freshwater for some        treatment. If you provide your own wa-

28                  www.BACKHOMEMAGAZINE.COM
ter or electricity, you’ll benefit directly   systems designed primarily to get rid         However, multiple side trips from
from lessening this burden.                  of greywater rather than extract value    this main path may apply to you. For
    • Plant growth. Greywater can sup-       from it. The “hardware” that accom-       example, a quick and dirty (instead of
port a flourishing landscape where           plishes this generally consists of:       carefully considered and optimized)
irrigation water might otherwise not            1. Greywater source(s): washing        approach is not necessarily wrong.
be available.                                machine, shower, bathtub, and/or          Greywater systems can be slapped
    • Reclamation of nutrients. Loss of      sinks.                                    together without much thought or
nutrients through wastewater disposal           2. Collection plumbing: pipes that     trouble—and the vast majority are.
into rivers or oceans is a subtle but        transport greywater from the house        Greywater work is pretty forgiving, so
highly significant form of erosion.          to one or more points just outside the    no matter how it gets done, you’ll real-
Reclaiming otherwise wasted nutrients        house.                                    ize a portion of the possible benefits.
in greywater helps maintain the land’s          3. Surge tank, filter, and pump:           If your system is to be for disposal
fertility.                                   optional elements that add complex-       only and not irrigation (for example,
    • Increased awareness of, and sensi-     ity and cost but make the distribution    to take the pressure off a septic sys-
tivity to, natural cycles. The greywater     plumbing’s job easier, especially for     tem), then information on optimizing
user, by having a reason to pay more         large flows.                               irrigation efficiency will concern you
attention to the annual progression of          4. Distribution plumbing: plumbing     only inasmuch as it helps you spread
the seasons, the circulation of water        that transports greywater through the     greywater over a wide area and avoid
between the Earth and the sky, and the       yard and divides it among plants.         overloading the soil with water.
needs of plants, benefits intangibly but         5. Receiving landscape: soil, roots,       If your system is to be retrofitted
greatly by participating directly in the     plants, and mulch basins that contain,    to an existing building, you’re pretty
wise husbandry of vital global nutrient      cover, purify, and use the greywater.     much stuck working with what you’ve
and water cycles.                               6. People: those who design, make,     got. But if it’s for new construction,
                                             and maintain the system, generate the     you have the opportunity to make
When Not to Use Greywater                    greywater, tend the garden, and eat       everything better integrated—a much
                                             the fruits.                               more challenging and potentially re-
   There are a number of possible rea-                                                 warding task.
sons not to use greywater, or to use it      Very Context-Dependent                        If permits are involved, you’ll need
only during certain times of year:                                                     to deal with legal requirements that
   • Insufficient space. In some situa-          A small change in your context—        push you to do impractical things. To
tions, neighbors are too close, or the       siting, sources, irrigation need, per-    get through this maze, you may choose
yard too small or nonexistent.               colation rate, etc.—can mean drastic      to arrange plumbing conventionally
   • Inaccessible drainpipes. If all         changes in your system selection and      first, to pass inspection, and then add
plumbing is entombed under a con-            design. Most individual systems will      greywater plumbing later. If you keep
crete slab, accessing most of the grey-      follow the middle path: a carefully       blackwater and greywater lines sepa-
water won’t be economical.                   considered and optimized do-it-your-      rate, installing a greywater system later
   • Unsuitable soil. Soil that is either    self residential retrofit system for      is easy.
extremely permeable or impermeable           gravity-flow irrigation, not too ritzy,        A failing septic leach field can be
may preclude the use of a greywater          built without a permit, in a moderate     restored to function by lowering or
system.                                      climate, with a plumber involved in       eliminating the flow of greywater
   • Legality concerns and/or permit         the collection plumbing, and a septic     through it. It is worth noting that sav-
hassles. In much of the industrial-          or sewer backup.                          ings on septic tank pumping and leach
ized world, the legality of greywater                                                  field replacement will pay for almost
systems is a “grey” area. However,           ELEMENTS OF GREYWATER SYSTEMS             any greywater system.
there seems to be movement toward
a less paranoid, more realistic official          Sink                                  A Few Assessments
attitude, concurrent with increased
experience and improved systems, not                                                       A site map is a great aid for de-
to mention water shortages and pollu-                                                  signing a system. A map with a scale
tion problems.                               Collection           People               of 1:100 with 1' contours is ideal. If
                                             plumbing                                  such a map is not available, make a
Elements of a Greywater System                                                         sketch showing the house, boundaries,
                                                                                       irrigated areas, natural water features,
   What a greywater system does is                                                     utility lines, routes of plumbing under
collect greywater, then divide and dis-                   Distribution                 the house, and so forth.
tribute the flow among planted areas.                      plumbing                         Evaluating your water resources is
Most of the systems are variations on                                                  important as well. The first question
this basic functionality, even those                Drain to Mulch Basin               for any human habitation is, Where

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                                                       put to 40 gal/person/day, or enough to
                                                                                                                How to Measure Perk
      An Introduction to Greywater                     water four mature fruit trees or a dozen              Dig holes to greywater discharge depth
                                                       shrubs in an average climate. Extreme                 (usually 6" to 12") in the locations you
                                                       conservation habits can cut production                wish to discharge it. Place stakes into
does the water come from? Ideally,                     to 5 gal/person/day.                                  the bottoms firmly. Mark reference el-
for minimum impact and long-term                          On your site map, note where the                   evations on the stakes and fill the holes
sustainability, rain should be the                     greywater sources are and (if they are                with water two to four times, measuring
primary water source, followed by                      not combined) how much of the total                   each time how many inches the water
greywater, followed by gravity-flow                     flow comes from each set of sources.                   drops in a given number of minutes.
spring or creek water, followed by well                Group fixtures that share a common                     When it drops the same amount in the
or municipal water. Wherever the water                 drain into subtotals (for example, the                same amount of time, a couple of times
comes from, note its characteristics and               bathroom sink, tub, and shower often                  in a row, that’s your perk measurement.
limitations.                                           share a drain), and note where their                  Convert the numbers to perk rate in
    If you aim to live ecologically, thor-             plumbing goes.                                        minutes/inch (3" in 60 minutes is 20
oughly explore conservation options                       Consider whether it is appropriate                 min/inch, for example), then refer to the
before turning to reuse. Because of                    to move any greywater sources (such                   chart on page 31 to see how much area
the unavoidable inefficiencies inherent                 as a washing machine), add an outdoor                 you need to treat that much water.
in greywater systems, the gain from                    shower, or take any other action to im-                   If it takes hours for the water to drop
reducing consumption with water-con-                   prove the fit of water sources to irriga-              at all, or the water vanishes as fast as
serving fixtures is always greater than                 tion need. The places where greywater                 you can fill the hole, or if the holes fill
that from reusing the water.                           is generated should ideally be high on                with water by themselves, you’ve got
    For any system in any context, I                   the property, so you can irrigate more                a problem! If the perk is super slow,
recommend doing at least a rough real-                 area by gravity.                                      consider a constructed wetland. If it
ity check to make sure the quantities                     You should also note variations                    is super fast, add compost, mulch, and
of output and intended use are in the                  in the population of water users. If                  plants that will develop a dense network
same ballpark. It is commonly assumed                  everyone goes away in the dry season                  of roots to help purify greywater on its
that however much greywater there is                   for an extended time, this obviously                  short journey through the soil.
and however much irrigation is needed,                 affects the system’s design; you won’t
they’ll magically match up. Even if                    want to set up water-loving plants to                level. You need to establish that there is
you don’t want to reuse the greywater,                 be irrigated by greywater only.                      enough fall to get from the greywater
it’s good to have an idea of how much                                                                       sources to destination plants with a
you’ve got in order to know if your                    Check Slopes and Elevations                          constant downhill slope (generally 1/4"
disposal/treatment area is big enough.                                                                      per foot, or 2 percent).
For most purposes, you can just take                      This step is crucial for collec-                     In the landscape, the pipes should
the home’s population and multiply it                  tion plumbing and gravity-powered                    ideally still be at surface level, and in
by an approximate daily use figure, as                  greywater distribution, especially                   no case more than 12" belowground.
shown in the chart below.                              branched-drain systems, where slopes                 For proper flow, drainpipes must in-
    Homes without water-conserving                     must be accurately measured.                         exorably get lower with distance from
fixtures generate about 55 gal/person/                     Check the slope from beginning to                 the source, and also with the negotia-
day. Efficient fixtures cut this daily out-              end of the intended system with a water              tion of each obstacle, change of pipe
                                                                                                            size, etc.—and the pipe elevation can’t
                                                                                                            ever go back up again.
                Greywater Sources by Quality and Quantity                                                      Note these elevations on your site
                                                                                                            map. From slope measurements, you
                                                                                                            can determine which sources can wa-
     Source            Quality                                 Quantity                                     ter which plants. Remember that you
     Washer            Good: Medium soap concentration         Large: 30-50 gal/load                        actually need a bit more than 2 percent
                                                                                                            slope from end to end, to allow for
     Dishwasher        Poor: High salt & pH, some solids       Small: 5-10 gal/load                         obstacles and other “fall eaters.”
     Kitchen sink      Good: High nutrients, but some grease   Large: 5-15 gal/person/day
                                                                                                            Check the Soil Perk
     Shower            Excellent: Minimal soap concentration   Large: 20 gal/person/day
     Tub               Excellent: Minimal soap concentration   Variable: 40 gal/adult, 25 gal/child            You should have at least an idea of
                                                                                                            the perk rate for any system. Quanti-
     Bathroom sink     Good: But higher soap concentration     Small: 1-5 gal/person/day                    tative measurement is necessary if a
                                                                                                            lot of greywater is going into a small
     Reverse-Osmosis   Excellent: Clearwater w/ no solids      Medium: 3-5 gal/gallon drinking water used   area, or the perk appears to be low, or
     water purifier                                                                                          the soil is clayey.

30                       www.BACKHOMEMAGAZINE.COM
    The rate at which water absorbs                         hand and it shows that the perk rate
                                                                                                            Health Considerations
into the soil—the percolation or perk                       is okay several feet down, it is surely     In practice, the health risk of greywater
rate—is an important variable in                            fine at greywater depth, but a free,         use has proved minimal. It is, after
greywater system design. High clay                          do-it-yourself perk test that takes an      all, the water you just bathed in and
content generally means slow perk,                          hour gives you better information (see      the residue from the clothes you just
which can get dramatically worse if                         sidebar “How to Measure Perk”).             wore not long ago. Despite all sorts of
you add salt-laden greywater. Rock can                                                                  grievous misuse, there has not been a
have slow or no perk. Very slow perk                        Gauge Your                                  single documented case of greywater-
can lead to standing water and noxious                      Treatment/Disposal Area                     transmitted illness in the United States.
smells. Sand is high perk, gravel more                                                                  Nonetheless, greywater may contain
so. Very fast perk can lead to ground-                         If you want only to dispose of grey-     infectious organisms, and it is poor
water contamination, though this is                         water, you can differentiate prospec-       practice to be constructing pathways for
unlikely if there is a dense network of                     tive treatment areas on your site map       infecting people.
plant roots.                                                by indicating how much greywater                All greywater safety guidelines stem
    It is vital to know about the perk                      they can handle. In this case, the only     from these two principles: (1) greywa-
where the greywater is going before                         concern is to not overload the soil or      ter must pass slowly through healthy
committing to a design. If you’re put-                      sensitive plants. Areas with higher perk    topsoil for natural purification to occur,
ting a small amount of greywater in a                       rate and areas with more wind and sun       and (2) systems must be designed so
big area, the only perk issue would be                      can take more water. You don’t want to      no greywater-to-human contact occurs
a really, really slow perk rate. If you                     apply too much water near the founda-       before purification. Some potential
have enough experience with your                            tion of the house.                          health-related issues and their solutions
soil—digging holes to various depths,                                                                   are listed below.
perhaps filling them with water, ob-                         Assess Your Irrigation Need                     Direct contact or consumption:
serving how water absorbs into the                                                                      Avoid cross-connections between
ground—to know it perks reasonably                              Note by different colors or shades      freshwater and greywater plumbing and
fast, you don’t need a perk test.                           the vegetation types and the extent of      wear gloves when cleaning greywater
    If you are applying a large amount                      irrigated areas and trees on your site      filters.
of greywater, or have a small area, or                      map, indicating areas of plants that            System overload: Do not include
are applying greywater subsurface, a                        like wetter conditions. Or you can          water used to launder soiled diapers in
perk test is critical. Based on the re-                     simply make a list of irrigated areas       the greywater supply, and don’t store
sult, you might change the size of the                      and how much water you think they           greywater for more than 24 hours.
system by a factor of four or more, or                      want. Again, if your aim is to live             Microorganisms on plants: Do not
even decide that a greywater system                         ecologically, you should thoroughly         apply greywater directly on lawns, or
is infeasible.                                              explore conservation options in the         to fruits and vegetables that are eaten
    A professional (read expensive)                         landscape before turning to reuse to        raw, such as lettuce, carrots, and straw-
perk test is required for installing                        feed water-hog plants.                      berries.
almost any septic system these days.                            Estimating irrigation demand is an          Microorganisms in respiratory
These tests are usually done with a                         inexact science. Even getting within        system: Do not recycle greywater with
truck-mounted borer to a depth that                         a factor of two of the real irrigation      sprinklers.
is irrelevant to greywater systems. If                      demand is an ambitious goal. As a               Chemical contamination: Avoid
you already have one of these tests in                      rough rule of thumb, figure that your        the use of nonbiodegradable (chemical)
                                                            plants need about 1/2 gallon per week       household cleaning products.
                                                            of water for each square foot of plant.         Contamination of surface water:
  Disposal Loading Rates                                    Double this figure for desert, and halve
                                                            it for a cool, humid climate. You can
                                                                                                        Discharge greywater underground or
                                                                                                        into a mulch-filled basin, and water
                                                            also double or halve this figure again       intermittently to avoid saturating the
    Infiltration rate,




                                                            for plants that use more or less water.     soil.
                        gal/day/sq. ft.



                                          sq. ft./gal/day
                                          Area needed,




                                                            For trees, calculate the area under the
                        Loading rate




                                                            canopy and multiply it by the gallons      Art Ludwig will continue with Part
    min/inch




                                                            per square foot per week.                  II of this article in the next issue of
                                                                This rule of thumb above does not      BACKHOME, where he will discuss the
                                                            account for variations in evapotrans-      practical aspects of branched-drain
     0-30                   2.5              0.4            piration rate by season, climate, plant    systems, radical plumbing, and mulch
                                                            type, seasonal loss of leaves, rainfall,   basin options. For more informa-
     40-45                  1.5              0.7            and irrigation efficiency. It does,        tion on the book Create an Oasis
     45-60                  1.0              1.0            however, land you more or less where       with Greywater see the review in
                                                            you’d end up if you did consider all       BACKHOME No. 85 (Nov/Dec 2006) or
     60-120                 0.5              2.0            those things.                              go to www.oasisdesign.net/greywater.

                                                                                                       BACKHOME MAGAZINE JAN/FEB 2007           31

								
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