If you're replacing a cesspool or building new in Kula, Pukalani or Makawao, your engineer will steer you toward one of a few approved wastewater systems. Each one needs different excavation and different upkeep for years afterward.
The options Hawaiʻi allows
The state Department of Health lists the approved individual wastewater system (IWS) technologies:
- Septic tanks.
- Aerobic treatment units (ATUs).
- Passive aerobic systems that still need a septic tank, such as Eljen or Presby.
- Bioreactor gardens.
- Composting toilets and incinerator toilets.
Most single-family homes end up with a septic tank or an aerobic unit, each feeding a soil absorption system.
Septic system: simpler, more digging
Under state law, a septic system is a tank, piping and a drainage field, where wastewater is naturally cleaned as it filters through soil. It has few moving parts. The tradeoff is space and soil: the leach field needs enough suitable ground, and on rocky or steep Upcountry lots that can mean a lot of hammering and fill.
Aerobic unit: better treatment, more upkeep
An aerobic treatment unit adds a tank with an aeration device that pumps oxygen in, so microbes break waste down further. Health Department material notes that aerobic systems provide secondary treatment, while septic tanks provide only primary treatment.
The catch is maintenance. State rules require ATU owners to keep an active service contract with a certified operator and to submit a copy to the Health Department every year. The contract must include checking the sludge level every six months and pumping when needed.
The Health Department notes that some homes need an aerobic unit instead of a septic tank because of the location or other site features.
When the standard options don't fit
A 2022 change to state law lets the Health Director approve other wastewater systems. It also lets the Director grant exemptions for legitimate reasons such as small lot size, steep topography, poor soils or access problems, all of which are common Upcountry.
The process
- Hire a Hawaiʻi-licensed civil engineer. This is the Health Department's own first step for any cesspool upgrade or new system.
- The engineer evaluates the site and designs the system. The application is filed online through the state's wastewater portal.
- A licensed contractor does the excavation and installation. See how to check a license.
- Inspection, then backfill.
Find septic installers in Upcountry or on the septic and cesspool page. Buying an Upcountry home? Ask what system it has before you make an offer. Listings at Real Estate for Sale Maui.