Multnomah County, OR Landscaping Rules: Rainwater Harvesting (2026)

Oregon is one of the most rainwater-friendly states in the US: ORS 537 confirms landowners may collect rainwater from rooftops for beneficial use without water rights. Multnomah County and Portland actively encourage rainwater harvesting as green infrastructure. Simple rain barrels (typically 50-100 gallons, non-pressurized, for garden/lawn irrigation) require no permits anywhere in the county. Larger cisterns, pressurized systems, or any system plumbed into the house must comply with Oregon Plumbing Specialty Code (OPSC, OAR 918-750) and the Uniform Plumbing Code Appendix M - typically triggering plumbing permits through Portland BDS or County Land Use. Potable use requires UV/filtration treatment meeting state health standards. Portland's Clean River Rewards program (PCC 17.36) offers stormwater utility bill discounts up to 35% for on-site rainwater management including rain gardens, eco-roofs, and rain barrels. Portland Ecoroof Program has incentivized over 550 vegetated roofs. Rainwater systems serving toilet flushing or cold-water laundry require backflow prevention on any city water cross-connection. HOAs may have visual screening requirements but cannot ban collection outright.