Rainwater Harvesting: Honolulu vs Mililani Town
How do rainwater harvesting rules compare between Honolulu, HI and Mililani Town, HI?
Honolulu and Mililani Town have similar restriction levels.
Honolulu, HI
Honolulu County
Honolulu County has no ordinance restricting residential rainwater harvesting; the Board of Water Supply encourages it countywide through a rain barrel rebate program and CTAHR catchment guidelines.
View full Honolulu rules →Mililani Town, HI
Honolulu County
Mililani Town residents can collect rainwater for outdoor use without a permit up to 360 gallons; HOA rules may affect visible barrel placement.
View full Mililani Town rules →Key Facts Comparison
| Fact | Honolulu | Mililani Town |
|---|---|---|
| County ordinance | None | - |
| Permit threshold | Up to 360 gallons exempt | 360 gallons storage |
| Rebate program | Board of Water Supply | - |
| Guidelines | UH CTAHR catchment program | - |
| State restrictions | None | - |
| Code reference | - | Hawaii Plumbing Code Ch. 16 |
| Rebates | - | BWS rain barrel program |
| HOA layer | - | MTA architectural rules |
Highlighted rows indicate differences between cities.
Honolulu FAQ
Do I need a permit for a backyard rain barrel on Oahu?
Usually no. Exterior catchment up to 360 gallons for outdoor irrigation is exempt under the Hawaii Plumbing Code, and Honolulu County has no separate ordinance.
Are there incentives for catching rainwater?
Yes. The Honolulu Board of Water Supply runs a rain barrel rebate program encouraging conservation. Details and eligibility are posted on the BWS website.
Mililani Town FAQ
Does Mililani Town Association allow rain barrels?
Generally yes, with placement and color guidelines. Submit an architectural application to the MTA before installation to avoid compliance letters.
Can I plumb rainwater to my Mililani washing machine?
Only with a plumbing permit and proper backflow protection. Non-potable indoor use is regulated under the Hawaii Plumbing Code.
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