Tuesday, July 21, 2009

The Cost of Urban Rainfall

Hamilton County, Ohio averages 42.6 inches of rainfall per year. Some of that falls on the more than 36,000 acres of impervious surfaces that keep our homes and businesses dry and provide driveways and parking for our automobiles. (This figure does not include roadways.) Since our sewers were designed to convey sewage and not rainfall flows, rain events frequently overcharge the infrastructure, and to relieve that we send about 6 Billion gallons of untreated combined rainfall and sewage into the Ohio river each year. The US Environmental Protection Agency doesn't permit that, and finally after decades of back and forth, they are making us enlarge our infrastructure to largely eliminate these "combined sewer overflows" - to the tune of $3 Billion dollars. That's serious change; the cost of urban rainfall would buy us a Hamilton County light rail system, estimated for the 2002 MetroMoves plan at $2.6 Billion. The cost of eliminating untreated sewage discharges doesn't generate the same interest and hype that rail transportation does... but that's a subject for another post.

Well nobody is suggesting that we shouldn't like rain, of course. But maybe we should make good use of it before it hits the ground, while it is in a relatively pure state, able to be moved by gravity - and before we have to pay for its expensive ride downhill to the Ohio river. How much water are we talking about? A lot. Remember the 42.6 inches falling each year on 36,000 acres of impervious surfaces in Hamilton County? That represents about 85% of all drinking water pumped by the greater Cincinnati water works each year. That's right, if we captured all of the rain falling on all our roofs and driveways and parking lots, and treated and used that water locally, we'd barely need the water works. That's just a thought exercise, but we should be able to water the petunias with that rainfall, and possibly flush our toilets, and save some money for us and some carbon for the planet. It's nothing more than recovering the common sense possessed by our grandparents.

I was happy to have the chance to pee recently in the urinal pictured above, which was flushed by rainwater harvested from the rooftop of this highrise apartment building in Seoul, Korea.
The alien - looking cartoon character above each urinal and toilet is the Korean's happy way of telling you that you are using rainfall to wash away your waste product, without first having to send it down to the Ohio river and back. This building is part of the Seoul "Star City" project, a complex of 4 luxury highrise apartment buildings. The Star City buildings harvest rainwater from their roofs and store it in a 2 meter deep subbasement.
That way, the Seoul sewer system doesn't handle the roughly 3000 cubic meters of rainfall generated annually by each building. Treatment is minimal - only a simple German manufactured self-cleaning screen to remove the rare large particle. The Star City complex also uses the stored rainfall to irrigate a lovely urban garden space.

Star City was only the first major new construction in Seoul to implement rainwater harvesting and local rainwater use. According to Professor Mooyoung Han from Seoul National University, Seoul is the first International "Rain City" to require, by way of regulation, that every new public building will implement rainwater harvesting. Since 2004, 21 other cities in Korea have declared similar regulations requiring rainfall harvesting. The simple logic of the idea is the fuel for its growth. They're learning as they go about how this approach can scale to other building sizes and configurations, and they are looking to figure out the right mix of incentives and regulation to push rainwater harvesting to all new private buildings, and to preexisting construction. They are moving toward solving their urban rainfall problems - similar in type to those in Cincinnati - not by costly expansion of their urban infrastructure, but by capturing and storing and using rainwater locally. This is more a problem of government and institutions and laws, than of engineering and science (though there's some of that, too).

There are lots of questions, but lots of motivation to try and get the answers. Can Cincinnati be the first U.S. "rain city"? Where would we start? How do we encourage broad scale participation by individual land owners? How much of that $3 Billion infrastructure expansion cost could we save, and how can we shift some of those funds over to help pay for local rainwater harvesting? How can we maintain the rainwater harvesting infrastructure, owned by individuals, over the long term?


  1. Jim, this makes too much sense. Therefore, it is a challenge to our God-given freedom as Americans, which entitles us to make the most brain-dead choices without any government regulations. Why are you advocating socialism? And why should we learn from foreigners?:-)

  2. Very interesting stuff, Jim. Neverthless, I'm glad no one saw you taking pictures in a bathroom.

  3. I think as the building design methods get modified to "go green" for saving electricity, they should combine some of these interesting "water conservation" ideas that you are describing to create a holistic approach. Perhaps a solar panel that doubles up for rainfall capture can be designed. Thanks for sharing your flush experience.

  4. A little TMI on the personal front but, environmentally, an excellent post. It makes a huge amount of sense and is the kind of thing we need to bring to scale. This is what the federal stimulus money should have been allocated to rather than highways.

  5. While the use of gray water for things like flushing toilets is interesting, we can reduce the need for this altogether in some instances like waterless urinals.

    A project that I worked on for Anyang, China included a rainwater collection system on the building's rooftop that would then filter down and water a green roof surface and continue on down through the highrise building providing a passive cooling system for the building's tenants.

  6. Ali, you are unfortunately right on track. I fear that even simple and logical ideas like this can get reduced to useless arguments between those who are oppressed and those who are (assumed to be) oppressors. The book I've been reading "Shop Class as Soulcraft: An Inquiry into the Value of Work" by Matt Crawford, has a lot to say about the roots of this I think, and I'm planning to post about that at some future point.

    Yea, I'm sorry about the TMI. But just remember it's all what's in your mind... And Wendy it is a funny experience to be in a bathroom with about 10 other people all taking pictures of toilets and urinals.

    The stimulus funding is a good point, Kaid. This is straightforward engineering. If you put an RFA on the streets for retrofitting existing buildings for rainwater harvesting with a one month deadline you'd get lots of offerors. Maybe the issue is the messy one of private ownership and how to select the properties in an equitable manner. Perhaps it would have been very useful to have a pilot program in the 50 largest cities where RWH is implemented in a select number of public buildings first... to serve as a seed for future implementation in privately owned properties.

    Sudhir and Randy great ideas. Randy that project in Anyang sounds really neat. It shows that if you think about the resources you have at your disposal in a slightly "out of the box" (or "off of the grid") way, there seem to be no end to the possibilities.

  7. Great Stuff Jim! I would love to find someone locally (Cincinnati), if they exist, to talk about possibilities of doing this on a smaller scale. We are renovating some historical buildings in OTR for a brewery and would love to find a way to feasibly capture the rain water for use in watering hops and other applications (non-consumption). If you have thoughts, I would love them. bryon@cincybeerco.com

  8. Right on, Jim! Whenever I read "energy efficiency" I translate that to "resource efficiency" and think of innovative (or simple, even traditional, as you alluded to) ways to conserve energy, water, materials, space, etc. I agree with you that, for rainwater harvesting, the will of the public and private sectors does seem to be the biggest hurdle to overcome.

  9. Hey Bryon,
    Anyone who is a beer baron is someone I must meet. With hundreds of thousands of individual parcels in Hamilton county, figuring out a way to do this on a small local scale is where the action is. I'll contact you separately to discuss how we might go about this.

    Debbie you and I are on the same page!

  10. "Show a man to fish...." How much would it cost to direct waste water from the rec center showers to water the Sigma Sigma Commons? Maybe the Marriott would be interested in routing some of their grey water to the Nursing School fountain/gardens? "Think globally - implement locally." Either would be great PR for UC SUE. Jim, would you be the PI? Any suggestions for funding mechanisms? Pamela Heckel