Help me design a reclaimed water irrigation system....

Peter SteinbergAugust 22, 2010

Hello all, I was hoping that you could help me put together the elements of a water reclamation system for my rooftop garden. Here are the specifics:

I have a carriage house in Brooklyn, NY. It has a 1,500 square foot roof. The roof is almost 100% covered with skylights, deck and planters. I'd say it's about 20% skylights, 60% deck, and 20% planters.

(Before anyone brings up a green roof, I went with a decked roof because I have no yard -- this roof is my only outdoor space, so ipe and pavers for me.)

Currently, there's a drip irrigation system that's attached to the city water supply. I, of course, pay for that water... and then pay again as the city charges a sewer charge that's dependent on the amount of water you use.

(This sewer charge galls me because the vast majority of water I use to irrigate never ends up in the sewer.)

Ok, next piece of background is that the drainage for my roof -- both rain and any overflow from the irrigation or occasional hose-watering runs to 2 downspouts and down the back of the house to a concrete paved area between me and the apartment building behind me. It all ends up in a ground drain that I suppose ultimately connects to the city sewer... although it drains so slowly that I think the pipe is collapsed and the water is just absorbed by the ground underneath my building and the building behind me.

So here's what I have in mind.

1. Some tanks or other storage behind my house that hold the water that comes off my roof. I actually have room for quite a few tanks. My land back there is the width of the house -- 50 feet -- and 5' deep. So I could connect up a long series of these tanks and hold a LOT of water.

2. A pump that sends the water back up to the roof whenever the irrigation system calls for water. The pump would have to energy efficient enough that I'm not paying a whole lot more for the electricity than I'm paying for the water. Also, because my house is 2 stories tall, and the area behind the house is down 1 excavated story, the pump will be sending the water up over 30'.

3. Some sort of valve/switch that recognizes when the tanks are empty and sends water from the city water instead.

Lastly, the acquisition and installation cost of the whole system has to be low enough that it pays for itself over a reasonable number of years.

So... any ideas? Anyone want to point me in the right direction or point out the flaws in my design?

Thanks in advance and no suggestion is too out there. Bring it on.

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What is your current usage for irrigation and its costs?

I doubt you can make a system that you can justify on economics. In my area, water + sewage costs run about 1.3 cents per gallon. Your irrigating ~300 sq/ft, with drip you should less than gallon or two per sqft per month. So there is not alot of potential savings.

    Bookmark   August 30, 2010 at 2:21PM
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A single 55 Gal watering system can be done between $100 - $200! (excluding pump)!

Where as we collect water into a 1200 gallon underground tank and use a shallow well jet pump for distribution to our five water stations. Initial installation costs were over $4,000 in material and I did the work! And I'm considering adding an additional 800-1200 gallon tank!

Your issues are going to be 1. What do your local building codes allow. 2. How large a tank can you use. 3. A large $$$ for you is going to be the size of the pump needed to pump water to the roof!

Hope this helps........

    Bookmark   September 28, 2010 at 9:29PM
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Perhaps I'm missing something here, but it strikes me as wasteful to let gravity take the rainwater from roof height to the ground, then use electricity to pump it back up. Can't you find a way to collect and store rainwater at roof level? Rain barrels are widely available. The collector could be something as simple as a tarp mounted on a simple frame, say, 8' above roof level, and angled downward to a big-box-store rain gutter.

    Bookmark   September 29, 2010 at 12:43AM
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The issue is going to be the weight of the water. At over 7 lbs / gallon, the weight will exceed the allowable roof load rather quickly!

    Bookmark   September 29, 2010 at 4:15PM
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