GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

What’s the best way to integrate rain water to a condo system?

motley_f0ol | Posted in Mechanicals on


First of thank you for having such a wonderful forum to share infornation on. I have found this place very usefull in the past.

To my question: im designing a 7 story medium sized condo that will house 6 families. Im thinking of integrating rain harvesting to the building as we some times get droughts and i hate to see all that rain water go to waste. I think it should be regulation to have some sort of backup water sytem just incase the mains dry up. But for now will just be using rain water for the watering closet.

Some numbers:

Avarage rainfall avarage per month 120 to 40 kg/m2 (65kg)
Yearly avarage rain fall: 775 kg/m2
Roof rain collection area: 250m2 (probably will only use half of this)
Wc water usage: 6 families, 3 people per avarage, 4 floushes per person(?), 6L per flush = 432L per day. (Woa!) 157,680L per year.
Cost of water in Istanbul Turkey: if under 10m3/ month per unit 3.7TL , if over 5.7TL
Area for south facing solar collectors 20m2: more on this maybe later

So im thinking that will have a larger tank burried in the garden some place for monthly rain fall and have a smaller tank on the roof for daily use as having too many large water tanks on the roof doesnt soud like a good idea. So a small 500L to 1000L tank on the roof and maybe a 20,000l one in the garden. I will be excavating alot for the foundation anyways. And on dry spells or for maintanace the 500l tank can be fed by the city main.

Its still at an inception phase so everything is up in the air right now and i was brain storming. What do you guys thing is if feasable? Profitabble? What should i consider?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    The technical challenges of rainwater harvesting systems and the use of cisterns have all been solved; the needed equipment is available. However, it's hard to know whether building codes in Istanbul allow these types of systems to be installed -- so of course you'll have to research your local code. Nor do I know whether the type of equipment that is manufactured in North America is available in Turkey. Finally, only you can perform the cost-effectiveness calculations to determine whether this type of system makes sense.

    I don't know whether these articles are relevant to your needs in Turkey, but here are some resources on the GBA web site:

    GBA Encyclopedia: Cisterns and Rain Barrels

    Water, Water Everywhere

    GBA Product Guide: Rainwater Harvesting

    Here are some other online resources:

    Rainwater Collection Information Sources

    Rainwater Harvesting: FAQ

  2. iLikeDirt | | #2

    In addition, you might think about going with low flow or dual-flush toilets. Some can be as low as 3.4 liters per flush, which would lower your projected yearly toilet water consumption figure to 89,352 liters. That would decrease the required size and cost of your graywater harvesting system, or allow more of the water it collects to irrigate landscape plants.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |