Help me design a water reclamation system

petestein1August 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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lehua49

Pete,
You have the main items for your system. It is basically a recirculation system with an added rainwater/house water supplement. Your idea is conceptual at this point but will begin to become more detailed with added data. What is your house pressure and flow? What are your plant water needs in other words what is your water demand for your garden per day or week? Are you keeping what you garden now or thinking of expanding? What is the vertical distance from where the barrels will sit to the top of the pots on the deck? You will need to have a backflow preventer or check valve outside the tank outlet to keep the line filled to the deck. This save pump usage and noise to fill the line each irrigation cycle. You will nee to connect all the tanks to each other to act as a larger reservoir for the pump, so level ground is a premium. You will need to settle out the impurities from the roof runoff water. This can be done with a filter after the pump or with an outlet above the bottom of the tank. Depending on the size of the tanks, you could stack smaller tanks on top of each other but they would have to be restrained somehow for safety. Except for free rain water, your recycle system will cost you electricity each time you pump it to the roof and has no relation to what you pay for city water. This pumping cost can be figured out when the pump design is finalized and you know the pump horsepower energy it will take to move water to the roof. Drip irrigation is the most efficient method of irrigation and will save you the most money and it will reduce your roof runoff therefore City water. You would want to pump exactly what the plants utilize and no more(no runoff). What is your average monthly rainfall? You usually design your pump system for peak flow. Full mature plants and highest evaporation periods plus a 10 to 20 % Assurance factor. That should get you started. If you need help getting the data let us know here at the forum. Aloha

    Bookmark   August 22, 2010 at 6:23PM
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Stewart_Yardley

I think the fact that you already have the intention to take the initiative to implement a water-saving measure, it is considered as a good start. As a consumer, I have to agree with you that water just seems so expensive today. There are like multiple charges for a single usage. However, there isn't much we can do to change the situation as the main supply is within our control. What we can do is to just try and conserve water from our end, which is at our homes.

    Bookmark   November 4, 2013 at 1:10AM
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