'Rainwater Harvesting' refers to the collection and storage of rain. Collection is usually from rooftops, and storage in catchment tanks. Stored water can be used for non-potable purposes such as irrigating lawns, washing cars, or flushing toilets. Rainwater harvesting systems can range from a simple barrel at the bottom of a downspout to multiple tanks with pumps and controls. Before the creation of public water utilities, rainwater harvesting provided water for many American homes. It is still popular in places with limited water resources such as island communities like Hawaii. While we think of ourselves as living in a rainy climate, recent drought conditions throughout Oregon remind us how quickly we can run short of water.

Using purified potable water for purposes like flushing toilets or irrigating landscape is a waste of a valuable resource. Portland residents are asking more questions about the role of conservation in extending the supply of drinking water. Stored water can substitute for piped drinking water for many uses where a high level of purity is not required.

Rainwater harvesting is also effective in reducing stormwater runoff pollution. When rain falls, it is clean, but it immediately picks up pollutants from rooftops and pavement. This pollution is carried into storm drains and then into streams. Collecting stormwater from rooftops and directing it to storage tanks so it can later be used for irrigation or flushing decreases the volume and rate of runoff. The City of Portland encourages on-site stormwater innovations and stormwater management fees are reduced if stormwater runoff is safely retained on-site.  In certain locations, Portland will pay an incentive for the disconnection of eligible downspouts from eastside combined sewers. Please call 503-823-5858 to find out if you have any eligible downspouts.  Click here to learn more about the downspout disconnect program. 

For residential projects:
You don't need any permits to use collected rainwater outside the house.

To use it indoors for purposes like toilet flushing, you'll need to apply for a permit. The permit guidelines show how to plumb separate lines for rainwater and city water, and prevent contamination between them. The permit guide can be downloaded here.

To go a step further and use rainwater to replace potable water, you'll need to apply for a permit appeal. The appeal process is used so that the Bureau of Development Services can look over your specific design and installation. It's not an adversarial appeal, more like a way to be sure an applicant has really thought through the installation. Also, that you understand the commitment--once water pipes have been used for rainwater they can't be converted back to city water.

For commercial/multifamily applications:
To use harvested rainwater to flush toilets, you are required to be treat the water with filters, UV and/or chlorinating (usually a combination of the first two and possibly all three). 

Portland Leads the Way

Residential and commercial rainwater harvesting systems are taking root in Portland. In 1996, urban ecologist innovators, Ole and Maitri Ersson built Portland's first permitted rainwater harvesting system to significantly supplement their residential water needs. The system is designed to harvest and purify rainwater for all of their water-related needs except during long dry summers when they are able to switch back to City water. Their 1,500-gallon system collects 27,000 gallons a year - effectively providing enough water for nine months out of the year. The system cost around $1,500.

In 2002, Matt and Kristin Bacon Brenes installed a state of the art 3,400-gallon system that provides water for all household uses, even drinking water. The system collects and stores enough water for all their water needs for 10 months a year and cost $7,000 to design and install.

 Pedro Ferbel's downspout/drum system demonstrates that harvesting can be very low tech as well.  Each downspout outflows into a simple 55-gallon drum with a hose-friendly spigot that makes it readily available for landscape irrigation.  The runoff from the north slope of the roof is harvested in a six drum stack configuration and the water is used to irrigate a densely planted permaculture garden that provides corn and other vegetables throughout the summer.

Portland developers have also taken the first steps towards incorporating rainwater harvesting in commercial buildings. Group Mackenzie and Systems Design Inc. designed the American Honda plant in Gresham to include a catchment and storage system for toilet flushing and high-efficiency irrigation. The system, which only uses a portion of the building's large roof area, helped earn the building LEED 'Gold' level certification.

 Epler Hall is a mixed-use classroom and dormitory building that moves rainwater from the roof and plaza to a ground level water feature before collecting it to flush seven first floor toilets and irrigate the landscape.  The system is expected to reduce the building's annual demand for municipally treated water by 110,660 gallons and associated annual costs by approximately $980.  

Station Place, a 13-story affordable housing tower, flushes 76 toilets on seven floors using a 20,000-gallon cistern. Annual water savings are expected to be 250,000 gallons.

Tall, urban buildings present a greater challenge to rainwater harvesting due to smaller roof area relative to water needs and the difficulty of including on-site storage tanks. To explore this barrier further, G/Rated hired Group Mackenzie and System Design Inc. to do a feasibility study for the new 12-story affordable housing tower in downtown Portland. The study found that rainwater harvesting was technically feasible, but would significantly increase capital and operational costs compared to conventional plumbing and potable water use.

Calculate Your Rainwater Harvesting Potential

If you're interested in rainwater harvesting at your home, here's how to estimate annual water supply:

Collection Area (sq. ft) x Rainfall (in/yr.)  / 12 (in/ft) = Cubic Feet of Water/Year

Cubic Feet/Year x 7.43 (Gallons/Cubic Foot) = Gallons/Year

For example, a 500 sq. ft roof that gets 36 in/yr. will produce 1,500 Cubic Feet or 11,145 Gallons of water per year.

PLEASE NOTE: this calculation is for horizontal areas and does not take into consideration system losses such as evaporation or leakage.

Code Requirements

The Bureau of Development Services has produced a prescriptive code guide that details how to design and build a residential rainwater harvesting system for permit approval. A permit is required to use rainwater indoors, and the details shown in the guide should ensure that rainwater stays separate from potable water. The City considers unfiltered rainwater non-potable or unsafe to drink. For commercial projects, the City reviews each system through the appeal process. See below for details.

Portland Residential Rainwater Harvesting Code Guide (Bureau of Development Services-BDS) 

Commercial Rainwater Harvesting: Ken Carlson 503-823-7255 

'Oregon Smart Guides' on rainwater harvesting and water conservation systems (i.e. gray water reuse).

Resources

Rain Barrel Guide (BES)

Rain Barrel Guide

Case Studies

People's Food Co-op Case Study

PSU Stephen Epler Hall Case Study

Rivas-Scott Case Study

Incentives and Grants

Community Watershed Stewardship Program (BES)

Clean River Rewards Program (BES)

Ecoroof Grant (BES)

Downspout Disconnect Program (BES)