Archive for the ‘Rainwater Harvesting’ Category

I’ve been looking into solutions for storing the rainwater we harvest from the roof, and there are all kinds of tanks out there.  The most cost-effective tanks seem to be polyethylene, which are not really the look I want so close to my house.  Other semi-expensive alternatives include: flat flexible ‘bladder’ tanks that fit under a deck or in the crawl space of a house; underground tanks that sit beneath a concrete slab or patio; and tall, flat ‘wall-like’ slim plastic tanks that can fit along a narrow walkway or other narrow space.

What I really like are colored-concrete and corrugated steel tanks.

 I finally found a website that got me excited about making a tank!  They are called Technicians for Sustainability, LLC  http://www.tfssolar.com/, consultants for green building solutions based in Phoenix, Az.  They make water tanks from large corrugated galvanized culvert pipe embedded in a concrete base. I emailed them, questioning how to really seal the intersection of the galvanized pipe and the concrete at the bottom of the tank.  They were wonderful, quickly emailing me back a description of how they make a watertight connection, along with product recommendations and encouragement. Here are some photos from their website.


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One rule of thumb I’ve come across is: for every 1,000 square feet of roof, one inch of rainfall can yield about 600 gallons of water.  Alternatively, this formula (which can be found on many websites) can be used:

Area of roof in sq. ft.  X inches of rainfall per year X 0.62  = gallons runoff per year

(Here’s a unit analysis for that formula: ft X ft X in/year X ft/12 inch X 7.48 gal/cu.ft.    So, 7.48/12 is where the 0.62 comes from.)

So for my ~1,200 square foot house, using an average of 29.7 inches of rain per year, I come up with roughly 22,000 gallons of harvestable water!  That’s a big tank!

1200 sq. ft. X 29.7 in./yr. X 0.62 = 22,096.8 gallons.

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