[Greenbuilding] rainwater storage & use model

[Bobbi Chukran]

Hi Reuben,

For over eleven years, my husband and I had a complete rainwater 
system, and used it for everything.  Washing, laundry, cooking, 
drinking, garden irrigation....everything.

If you have a formula that tells you how many gallons you can catch, 
then you can assume that 100% of the rain hitting your roof will be 
caught.  Of course there is some "bounce back" but in general you'll 
catch it all.

And you'll be surprised at how much you catch from drizzling rain, 
and even from dew on the roof.

The KEY to how  much you're catch is how large your roof is.  I would 
also suggest that if at all possible, use a metal roof.  Asphalt 
roofs release petroleum products that you don't want in your water. 
And it's very handy to know how much your family uses on an annual 
basis, too.

We had two tanks for a total of 17,000 gallons for the two of us. 
Here in Texas, we only ran out of water once in all that time, and 
then only for a few months.  You might want to check to see if 
there's a good back-up in case you run out....we bought ours from the 
local city, and the water tasted horrible, but at least we had some. 
The price was very reasonable to buy it from them.

Good luck on your system.....we recently moved to town and now have 
city water again.  YUCK!  LOL.    My husband is still mourning the 
loss of all that rainwater.

One thing we did learn is that you'll have more cleaning chores to do 
with the system.  Not only for the filters and such, but also in the 
house.  Since we didn't treat our water with chlorine (we used a UV 
system), the showers and toilets did grow a bit of mold and the 
washing machine smelled a bit musty.  But I just cleaned more often.

Any other questions, feel free to e-mail us.

bobbi c.
down in texas



>I've built a spreadsheet model that uses daily rainfall on site, daily
>indoor (municipal) water usage, roof area, and a multiplier (currently 0.7)
>for system losses, to estimate what storage volume I'd need to bridge our
>90+day summer with little rain. My goal is to use no municipal water at all,
and to have adequate but not excessive storage.