Rainwater Harvesting: Honolulu vs Mililani Mauka
How do rainwater harvesting rules compare between Honolulu, HI and Mililani Mauka, HI?
Honolulu and Mililani Mauka 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 Mauka, HI
Honolulu County
Mililani Mauka homeowners may install rain barrels without a Honolulu permit; small outdoor catchment up to 360 gallons is exempt under state plumbing code.
View full Mililani Mauka rules →Key Facts Comparison
| Fact | Honolulu | Mililani Mauka |
|---|---|---|
| County ordinance | None | - |
| Permit threshold | Up to 360 gallons exempt | - |
| Rebate program | Board of Water Supply | - |
| Guidelines | UH CTAHR catchment program | - |
| State restrictions | None | - |
| City code | - | No specific ordinance |
| Plumbing code | - | Up to 360 gallons exempt |
| Incentive | - | BWS rebate programs |
| HOA layer | - | Mauka design review |
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 Mauka FAQ
Do I need a permit for a rain barrel in Mililani Mauka?
No. Residential catchment under 360 gallons is exempt under the Hawaii Plumbing Code, and Honolulu has no specific residential catchment ordinance.
Will the Mauka HOA let me install a rain barrel?
Usually yes with screening. Submit your plans to the Mililani Mauka Community Association architectural review to confirm placement and color requirements.
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