[permaculture] Watson Wick Design Spec's

Kirby Fry peace at totalaccess.net
Thu Oct 3 07:04:45 EDT 2002

Hi Jamie,

Yes, I was referring to a Watson Wick.  I've installed about five of these systems and they all seem to do very well if built properly.  Below is a post I sent to someone inquiring about a Watson wick.  Please let me know if you have any questions.

* * * * *

Black Range Lodge in Kingston, NM (see our permaculture resources web pages) is in touch with Tom Watson - designer of the pumice wick.  Tom lives in Embudo, NM and usually likes folks to attend a course before attempting to install one of these systems on their own.  They're very simple systems yet when you're dealing with lots and lots of human waste the smallest mistake can come back to haunt you ten fold.  He also does private consultations and Black Range frequently offers courses.

In Texas, the wick (if properly engineered and certified) can be legally sandwiched between a certified septic tank and a leach field.  The advantage of this is that you can harvest the water to sustain an orchard before it reaches your leach field which is required to be covered with only shallow rooted grasses - to prevent root penetration and damage to the leaky pipe that make up a leach line.

A standard septic system will run you between $1,500 and $2,500.  To do the wick legally would probably run you another $600 on top of the first figure.  
If a wick was all that you were using, off of the books, you could install it as a stand alone system for about the same or a little more.
That said, I'll give you some spec.'s on the wick, and then you can decide what your next step should be.  The wick is a gravel filled bed roughly 16' long x 16' wide x 2' deep.  The shape is merely a factor of the wick's surface area square footage - approx. 250 square feet per 4 persons.  
The wick should be strategically situated to perform as many functions as possible.  Of course, it should be down hill from the house, so that it may work on gravity and not rely on electricity and pumps.  It could serve as a wind break, hedge-row, deciduous or evergreen cover for an exposed side of the house and, or a site for fencing in a cellular foraging system for small livestock (i.e. fenced in sections where small livestock like chickens, can be let in and put out at key times).
Tom recommends using a porous aggregate like pumice or lava rock with 1/4" passageways between the aggregate.  Substitutions are frequently made if you don't live near a cinder cone where they mine pumice.  We use a 3/8" crushed limestone in these parts.
The bed often does not absorb all of the water and you must also install an overflow and a lagoon.  As the plants you put in the bed mature, the wick plants will transpire more and more water.  As a stand alone system it is not complete without heavy evergreen planting.
Our wick 2 years after installation absorbs all water in the summer, but still overflows in the winter, especially with heavy washing machine usage.

With the spoils from your excavation you can create a slight berm above the wick to prevent run off from inundating the system.  The rest can be used well below the wick as a berm / dam for your run off lagoon.  The lagoon is preferably NOT upwind from your house.  Save enough spoils to cover the wick with 6" of soil.
The waste line, usually a 4' PVC pipe, enters into a biodiffuser.  The diffuser is a black cage readily available at a septic tank vendor's yard.  It looks like a 55 gallon barrel cut in half, the sides of which are lined with vent slits to let the water exit and keep silt and sand out.
The bed is first filled with 2" of gravel, then the diffuser is set on that layer of gravel.  The diffuser can be set anywhere in the bed.  Near the sewer line entry point (fewer linear feet of drain line required) or in the center is what I usually shoot for.  Plum the 4" waste line into the diffuser.
The water level in the wick (determined by the height of the drain) should be at about half of the height of the diffuser.  You do not want to completely inundate the diffuser because the system is aerobic and would cease to be so if it were completely under water.  This means you have to level over from the diffuser to your drain outlet and set your drain height six inches or so above the bottom of the diffuser.

Cover the diffuser with a permeable landscaping cloth or frost cloth to prevent loose soil from entering into the diffuser chamber - not a must.  Fill bed with gravel except for the last six inches.  Fill the remainder of the wick with the spoils from your excavation.  Some granite sand and organic soil amendments (i.e. N, P, K, Mg) should also be added to the surface soils of the wick.  Nitrogen, of course, is readily available from the flow of nutrients from the house, but many plants must first get established in the dry upper 10" of soil.  The other amendments are necessary for a quick and robust response from fruiting plants.

Plant the wick with fruit trees, evergreen grasses and shrubs (i.e. bamboo) and even ornamental succulents (i.e. ginger lilies and others, gladiola, elephant ear, etc), many of which have edible and beneficial properties though you shouldn't eat the foliage of plants from the wick or lagoon - fruit is okay though.
As you can see now, there's a lot to consider.  If you like, give us a ring and we can talk in more detail.  Take care,

Kirby Fry
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