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help to start suburban grey water system at home, sandy soil  RSS feed

 
Francien Potgieter
Posts: 1
Location: Cape Town, South Africa
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I am new to this forum and new to designing grey water systems. Please let me know if i post this in the wrong place.

I live in Cape Town, South Africa and would like some help to start a grey water system at home. (normal suburban plot, very sandy soil as i am near the Atlantic ocean)

I have a slope running down (at approximately 5 degree angle) towards the area where i plan to have my food forest. My plan is to use water from the bath, shower and sink to water at least part of the garden. We are going through a drought phase and i am looking for an effective method to reuse the water. I am also going to install several rainwater tanks as it is our rainy season now and i don't want the water to go to the storm water drainage system if i can use it on my property.

I want to use some of the rain water to use in the toilet.

I need advice on filtering the water for either purpose.
 
Laura Allen
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Hi Francien,

Sounds like you have the perfect site for a gravity flow greywater system!

And it sounds like a simple type of greywater system would be a good match for your home/landscape.

With a simple greywater system the only filter you need will be in the landscape. You'll create what are called "mulch basins," shallow depressions in the soil that are filled with wood chips, this is where you'll direct greywater to be filtered by the wood chips. The mulch basins act as a filter and a sponge, and also spread out the water to cover more of the root zone of the plant.

I describe how to design and install a few systems that may work for you in my book, Greywater, Green Landscape. Unfortunately it would take too much text and images to post how to do it in this forum, so I'll just give you a few more resources to seek out. I'm part of an organization called Greywater Action and we have a bunch of on-line resources including webinar and downloadable manuals. In particular, I'd recommend you view the webinar about branched drain systems https://greywateraction.org/greywater-webinar-recordings/#Gravity-Flow,%20Branched%20Drain%20Systems%20and%20Greywater%20Irrigation%20in%20Arid%20Climates

http://www.greywateraction.org

Using rainwater for toilet flushing does require filtration. You'll most likely want to get a professional involved since you'll need to clean the water and make sure you've adequately protected the potable water supply. An improperly design system could create a "cross connection," where non-potable rainwater (imagine animal feces on the roof being flushing into system) is unintentionally mixed with the potable supply, contaminating the potable water.  One form of protection against cross connection is to just have a separate system you connect to, and when the tank runs out you manually switch over to the municipal supply. Other options include using an air-gap and refilling the tank with the municipal supply, or using a reduced pressure principal device. Your local regulators will most likely require one method or the other; you should check. The rainwater will need to be clean enough so grit and debris don't get into the toilet tank and interfere with the flush mechanisms.

Here is an excerpt from my book The Water-Wise Home that give you some specific details:
From The Water-Wise Home:

Sample Treatment Methods for Indoor Use of Rainwater

Specific filtration and disinfection requirements are determined by local regulations and installer preferences, but here are some common treatment methods for different end uses:

Toilet
▪ Filtration: Minimum 50-micron sediment filter (prevents grit from interfering with toilet valves)
▪ Optional: Carbon filter to address any color or odor issues
▪ Permitting agencies may require 5-micron filters and disinfection


Hope this helps!
 
Peter VanDerWal
Posts: 72
Location: Southern Arizona
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I would not bother trying to use either grey water or rain water for your toilet, it would be a waste of time and resources.  Anything that goes down the toilet is gone for all practical purposes so why bother using rain water?

Rain water is an excellent resource for watering your garden, unless you can collect so much that you can't use it all on the garden, why waste it anywhere else?  The same goes for grey water.

Until you get to the point where you have an abundance of rain/grey water and can't use it all in the garden, it's pointless to try using it anywhere else.  Think about it, if you want to use it in the toilet you are going to have to build filters etc. which will require time and materials (money) then you will have ongoing maintenance of those filters (more time and resources), plus you will have to add new plumbing, seperate from your existing plumbing, to route this water to your toilets.  Either that or fill your toilets from buckets (more time and resources).  After you go through all of that, what do you gain?

 
Laura Allen
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Peter VanDerWal wrote:I would not bother trying to use either grey water or rain water for your toilet, it would be a waste of time and resources.  Anything that goes down the toilet is gone for all practical purposes so why bother using rain water?

Rain water is an excellent resource for watering your garden, unless you can collect so much that you can't use it all on the garden, why waste it anywhere else?  The same goes for grey water.

Until you get to the point where you have an abundance of rain/grey water and can't use it all in the garden, it's pointless to try using it anywhere else.  Think about it, if you want to use it in the toilet you are going to have to build filters etc. which will require time and materials (money) then you will have ongoing maintenance of those filters (more time and resources), plus you will have to add new plumbing, seperate from your existing plumbing, to route this water to your toilets.  Either that or fill your toilets from buckets (more time and resources).  After you go through all of that, what do you gain?



Good point! You should first calculate how much irrigation demand you'll have and then see if you can match it with greywater and rainwater. I also wouldn't pursue a rainwater-to-toilet system unless you have more of it than you need for irrigation.
 
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