grey water marsh in a dry climate a bad idea?

Some authorities consider a greywater marsh to be a bad way of disposing of greywater in a dry climate. Is this so? I like the idea of a marsh since the resulting water can be stored, or used on vegetable gardens without worries. How much water would the marsh actually evaporate? And could the products of the marsh be valuable enough to counterbalance this?

I think this would depend on a number of things, including:

--how much greywater you are venting to the marsh - in a dryland, you have more evaporation than in more humid climates, so you would lose some of the moisture to the air. You would therefore need a fair amount of daily greywater to keep the spot "marshy" in the heat of summer. I know here in Phoenix - our evaporation rate is so high most of the year, a marsh would only be feasible if an entire community's greywater were pumped into it (and in fact, the City of Phoenix does create riparian areas including marshes from city wastewater). It's a much more efficient use of graywater for us here to get it into the soil - preferably soil covered with a lot of organic matter and shaded by plantings.

--You could lessen evaporation by making the marsh smaller, having tree canopy over the top, or trellises to shade it, etc. You can find out what your average monthly evaporation is here: http://www.wrcc.dri.edu/htmlfiles/westevap.final.html

--Or you could skip the marsh and vent the greywater directly to planting areas filled with woody plants.

Sometimes you just have to experiment to see what works for you on your property with the elements you have on hand and the functions you want them to perform. Do you know of anyone in Denver who has a marsh that you could talk to? They'd probably have the best advice for you.

Hello Jennifer,

Thanks for the answer.

For hypothetical situation like my own, I can't see any other way of going about it. (Greywater is illegal here in Colorado; but I want to design a greywater system in, so that when/if it becomes legal, it is already a functional part of my design.)

I would want to water annual vegetables, since they are the most water hungry part of the design. Raw greywater can't really do that.

I don't always have to water; we can get two inch downpours, and not have to water a well designed landscape for a few weeks. So I would want to store rain and grey water in a gravel filled pond, for dry periods. This climate has HUGE extremes of all sorts, and a main part of my design is to even them all out. Raw greywater can't be stored, except in the soil. And a fairly clayey soil basin being supplied with greywater just before a two inch downpour seems like a disaster waiting to happen.

Any other method of using it would be complicated and expensive (underground distribution) or have a potential ick factor for fussy neighbors. And if that potential was converted to reality just once— I would be in trouble.

Finally, I would want the whole of my small lot stuffed with edibles in every layer; thus the danger of raw greywater in a mulch basin touching edible leaves and fruits.

As far as volume, the system is being designed for a household of eight on a smallish lot.

And due to the current illegality of greywater, I don't know of anyone who has a functioning system.

It's a great idea. It's how the EthelM factory gets rid of its waste process water in Las Vegas. They are very proud of this and show it off on the tour. It's the second best part of the tour, the best part being the sample candies -- yum!

John Elliott wrote:It's a great idea. It's how the EthelM factory gets rid of its waste process water in Las Vegas. They are very proud of this and show it off on the tour. It's the second best part of the tour, the best part being the sample candies -- yum!

Hmmm....John, you may have just done my waistline a huge favor by pairing greywater and candy samples in the same response!

Hey Gilbert:

8 people's greywater on a smallish property is a goodly amount of water. I either forgot or didn't know CO also bans greywater collection as well as rainwater. Some day those laws will be reversed!

I'm wondering if you couldn't set up a system similar to John Todd's living machines where greywater is passed through several different "living" systems that filter it and then the clean water could be used for garden beds - the beds could even be "wicking beds" which mimic the look of the living machine containers so that it all looks like one big, robust, GREEN productive system. Should someone ever "narc" on you, you could simply disconnect the greywater part and still retain the rest. My friend Chip has a couple versions of living machines and they perform quite well.

Here's a video of John Todd describing living machines: (search John Todd on Youtube for other really great vids on this)



Here's a video of wicking beds made with IBC containers (which you can "pretty up" by painting or building wood boxes around by salvaging some old wooden pallets):



Here's a link to the free copy of "Toolbox for Sustainable City Living: A Do-It-Ourselves Guide" - they have a chapter on filtering greywater (this project is in Austin) Chapters 2 (Water), 3 (Waste) and 5 (Bioremediation) would be most helpful to you for this project.

This could turn out to be quite a magical, beautiful project! Keep us posted.

Thanks for all the great answers. I will have to look into those living machines some more, they look really neat.

I followed the evaporation link, and found that in the hottest month, I could expect to lose seven inches of water of any exposed surface. Presumably plants can transpire that much, as well. But in most months, it would be much lower, due to the fairly cool temperatures here.

But I suddenly saw all this in a different light. That much water will not be lost in a day, but in a month. The more I can get that water to do in the interim, the better. So, if I ran the water through a greywater marsh, then into a small shaded pond for ducks, and then after three days ran now nitrogen rich water into mulched garden beds, most of the seven inches would be transpired off the garden beds; where that much would have transpired off anyway. In six days about 1.3 inches will evaporate off the marsh and pond. The pond can be deep rather than shallow, and shaded, to minimize the effect. And the water was 'free' anyway, to start with. So, if I just ran the untreated water into a tree basin, I would have used it to grow a tree. This way I will have used it to grow marsh plants, keep ducks, raise azolla in a duck free corner of the duck pond, and irrigate and fertilize the garden. That sounds pretty good. There are lots of useful plants I could get from a marsh.

Another question; would a wood chip/ fungi filter bed do as good a job as a reed bed, while loosing less water?

And another; can a greywater marsh be shaded, and still function optimally?

It sounded like the pan evaporation analysis was done in full sun. Here, the sun is really intense due to a lack of air, but the air itself is fairly cool. So if I shaded it water and or plants, there should be a big difference.

Gilbert Fritz wrote: I followed the evaporation link, and found that in the hottest month, I could expect to lose seven inches of water of any exposed surface. Presumably plants can transpire that much, as well. But in most months, it would be much lower, due to the fairly cool temperatures here.

But I suddenly saw all this in a different light. That much water will not be lost in a day, but in a month. The more I can get that water to do in the interim, the better. So, if I ran the water through a greywater marsh, then into a small shaded pond for ducks, and then after three days ran now nitrogen rich water into mulched garden beds, most of the seven inches would be transpired off the garden beds; where that much would have transpired off anyway. In six days about 1.3 inches will evaporate off the marsh and pond. The pond can be deep rather than shallow, and shaded, to minimize the effect. And the water was 'free' anyway, to start with. So, if I just ran the untreated water into a tree basin, I would have used it to grow a tree. This way I will have used it to grow marsh plants, keep ducks, raise azolla in a duck free corner of the duck pond, and irrigate and fertilize the garden. That sounds pretty good. There are lots of useful plants I could get from a marsh.

Gilbert - your post made me smile - looks like Brad's book made an impression - esp. the part about running water through the longest possible path! I think if you have the wherewithal to set up that system, it would work fine. It might need tweaking from time to time, but all of this is a learning process.

Gilbert Fritz wrote:Another question; would a wood chip/ fungi filter bed do as good a job as a reed bed, while loosing less water?

Short answer: "maybe" - simply because there may be more micro-spaces in woody mulch to hold moisture. And the wood would also decay, making awesome humus over time.

You know, one of the "best practices" for "dark grey water" (aka "kitchen sink water") is to run it through a wood chip filter - basically a 55 gallon drum filled with woodchips that filters the nutrients and grease common in dark grey water before it enters the next system. The problem? It can get smelly. However, it does have the added advantage of attracting insects Because of this propensity, I know Scott Kellogg (Toolkit for Sustainable City Living) would empty the woodchips in with his hens and they would "process" the insects and other goodies they might find. Right now there seems to be a "clash of the titans" regarding the necessity for the wood chip filter. Brad thinks its overkill and stinky. And I will tell you here that my dark grey water does NOT go into a wood chip filter first, but gets direct right to an underground infiltration basin. The area around the underground infiltration basin IS filled with woodchips, however.

Gilbert Fritz wrote:And another; can a greywater marsh be shaded, and still function optimally?

Short answer: Yes. Especially in certain climates (drylands, high altitudes, etc). In fact, this is sometimes the only way they can stay "marshy".

Gilbert Fritz wrote:It sounded like the pan evaporation analysis was done in full sun. Here, the sun is really intense due to a lack of air, but the air itself is fairly cool. So if I shaded it water and or plants, there should be a big difference.

Yep - shading will help keep that moisture in place. Also, trees especially, create their own localized humidity which will also help keep things moister.

Please tell me you are taking lots of "before" pics and blogging about your thought process and progress!

I haven't made any changes to my property yet, so there is still time to take some before pictures. Once I get started, I will begin a new thread in the projects forum. Until the middle of March, I will be working on my design. I am using Edible Forest Gardens to guide my design process, but I am also influenced heavily by Brad Lancaster. He really clarified for me the point that water is NOT like oil, which can only be used once. I really want to be sure that all parts of my project will work together optimally BEFORE I start tearing up the lawn.

Edited to add: I am thinking about setting up as a small area of wood chips in a landscape fabric barrier, which any greywater would flow through before it reached the marsh. This would get around the difficult task of deconstructing the wetland every five years and cleaning it out, since most of the organic matter, lint, etc. should end up in the wood chips. These could be shoveled out once a year or so and composted. Much better than digging out gravel tied together with plant roots. And the greywater system would not have to be down for very much time.

Gilbert Fritz wrote:Hello Jennifer,

Thanks for the answer.

For hypothetical situation like my own, I can't see any other way of going about it. (Greywater is illegal here in Colorado; but I want to design a greywater system in, so that when/if it becomes legal, it is already a functional part of my design.)

I would want to water annual vegetables, since they are the most water hungry part of the design. Raw greywater can't really do that.

I don't always have to water; we can get two inch downpours, and not have to water a well designed landscape for a few weeks. So I would want to store rain and grey water in a gravel filled pond, for dry periods. This climate has HUGE extremes of all sorts, and a main part of my design is to even them all out. Raw greywater can't be stored, except in the soil. And a fairly clayey soil basin being supplied with greywater just before a two inch downpour seems like a disaster waiting to happen.

Any other method of using it would be complicated and expensive (underground distribution) or have a potential ick factor for fussy neighbors. And if that potential was converted to reality just once— I would be in trouble.

Finally, I would want the whole of my small lot stuffed with edibles in every layer; thus the danger of raw greywater in a mulch basin touching edible leaves and fruits.

As far as volume, the system is being designed for a household of eight on a smallish lot.

And due to the current illegality of greywater, I don't know of anyone who has a functioning system.

Are you confusing Grey water with Black water (Sewage) Grey water can be used in Colorado but you may not store it per say Water in Colorado can only be used once so if you wash your clothes in it you can not water your plants with it. However if you want to dig a trench and run it by your plants that is acceptable if you trench just so happens to go in to a sump but is allowed to seep out that is also acceptable. I know it is a play on words but that is the legal system for you! So long as if someone should ask you just say you are not directly watering plant with it you are ok. Also Cesspools are legal in CO. or now called On-site Wastewater Treatment! If you want to say it is a Natural Filtration system you can use that term too!