Rainwater harvesting is the accumulation and deposition of rainwater for reuse before it reaches the aquifer. Uses include water for garden, water for livestock, water for irrigation, and indoor heating for houses etc. In many places the water collected is just redirected to a deep pit with percolation. The harvested water can be used as drinking water as well as for storage and other purpose like irrigation.

Rainwater harvesting provides an independent water supply during regional water restrictions and in developed countries is often used to supplement the main supply. It provides water when there is a drought, can help mitigate flooding of low-lying areas, and reduces demand on wells which may enable groundwater levels to be sustained. It also helps in the availability of potable water as rainwater is substantially free of salinity and other salts.

The quality of collected rainwater is generally better than that of surface water. Contamination is always possible by airborne dust and mists, bird feces, and other debris, so some treatment may be necessary, depending on how the water will be used. – Wikipedia

In OREGON, the collection of rainwater is regulated:

In Oregon, only roof surfaces may be used for harvesting rainwater.

The City of Portland, Oregon, requires a minimum cistern capacity of 1,500 gallons capable of being filled with harvested rainwater or municipal water, with a reduced pressure backflow device and an air gap protecting the municipal supply from cross-connectio.

Statutes: Oregon’s New ‘Reach Code’ Utilizes IAPMO’s Green Plumbing and Mechanical Code Supplement. The “Reach Code,” established in Senate Bill 79 (2009), requires the State of Oregon Building Codes Division to adopt a code encompassing construction methods and technology designed to increase energy and water efficiency over the mandatory codes for builders that choose to incorporate them. Chapter 7 of the code, “Water Resource Conservation and Efficiency,” is based upon the 2010 IAPMO Green Plumbing and Mechanical Code Supplement, a tool designed to be used as an overlay to any building code to provide code officials with comprehensive, progressive and enforceable green provisions toward sustainable construction practices.

Taxes: No state tax incentives in place.

Highlights from the Oregon Smart Guide

There is no perfect one-size-fi ts-all tank and a backup water supply should always be available to charge the system when needed. Ideally a system should be large enough so there is little or no overflow loss during peak rainfall months and there is enough storage capacity for future demand. Determine the size of the tank needed by considering the expected water use, the capture potential (catchment area times rainfall times 0.46 equals gallons expected or capture potential), and the average monthly rainfall.

For example, a family of four will have an average demand of 200 gallons per day, using 50 gallons per person per day. They will require about 6,200 gallons a month. In the Salem example, December has the highest average monthly rainfall at 6.8 inches. Using the earlier formula, we can anticipate collecting 6,256 gallons of water in December. Supplying all of the family’s water needs for December will require a storage capacity of at least 6,200 gallons. July has the lowest rainfall with an average of 0.6 inches. Using the capture potential formula, we can expect to catch 552 gallons of water for July. Subtracting the 6,200-gallon monthly demand, the family of four will need at least 5,648 gallons of water in storage to meet the demand just for the month of July.

Based on Salem’s average monthly rainfall of 3.24 inches, the example’s 2,000-square-foot catchment area will collect about 3,202 gallons a month – not enough to meet the 6,200-gallons needed. Therefore, a reserve of water from peak rain months is necessary. For the example home, a storage capacity of between 8,000 to 10,000 gallons would allow water to be stored from the wetter months, with little overflow loss, forming a reserve for lower harvest months. A larger storage capacity also allows for a surplus to address long periods of drought between rain events.

Permits and Regulations
Small residential rainwater harvesting systems (less than 5,000 gallons) used for outside irrigation only that do not alter the existing private stormwater system generally do not require a permit. Larger or more complex systems used for irrigation may require building permit and storm water review. Such systems should not be connected to the public water system unless backflow protection is installed. Contact
the Eugene Water & Electric Board (EWEB) for more information.

To use rainwater for indoor nonpotable uses, like flushing toilets and clothes washing, you’ll need to apply for:

  • A plumbing permit to prevent contamination of drinking water;
  • An electrical permit for the pump or other electrical controls;
  • Building permits for cistern or underground tank installation may be required.

Grading or erosion control review may also be needed for
underground tanks.

To use rainwater for drinking water, you’ll need to apply for the permits described above and meet standards set by the Oregon Building Codes Division. The water must be treated to meet Federal safe drinking water standards.

First you’re going to need to capture it, then filter it, then store it.