Hawaii Cesspool Conversion Guide

Hawaii law requires every cesspool in the state to be converted by 2050. If your home has one, this guide covers what the law actually says, what converting costs, what your options are, and what financial help exists right now — in plain language, from a local company that works on cesspools every week.

In 2017, Hawaii passed Act 125, which requires every cesspool in the state to be upgraded, converted, or connected to a sewer system by January 1, 2050. Hawaii was also the first state to ban new cesspools, back in 2016.

The reason is scale. Hawaii has roughly 88,000 cesspools — more than any other state — and every one of them releases untreated sewage directly into the ground. On Oʻahu alone, the Hawaiʻi Department of Health counts more than 11,000 cesspools, together putting an estimated 7.5 million gallons of untreated wastewater into the ground every day. That wastewater does not disappear: it moves into groundwater, where much of our drinking water comes from, and out to the reefs and beaches.

Nobody loves the price tag, but the direction is set. The cesspool era in Hawaii is ending — the only question for homeowners is when, and on what terms.

Many Oʻahu homeowners honestly are not sure what is under their yard. There are a few ways to find out:

For a walkthrough — what to look for in the yard, on the water bill and in the records — read cesspool, septic or sewer: which do I have?

Every cesspool in Hawaiʻi now carries a priority level, and it is the one thing on the map that changes what the 2050 requirement means for you. Two systems have used the same numbers, so it is worth knowing which one you are looking at.

The 2017 report. Act 125 told the Department of Health to rank cesspools for replacement. Its 2017 report to the Legislature flagged 14 areas of the state and sorted them into four categories: Priority 1, areas where cesspools present a significant risk of human impacts, drinking water impacts, or draining to sensitive waters; Priority 2, areas with the potential to impact drinking water; Priority 3, areas with the potential to impact sensitive waters; and Priority 4, a placeholder for every cesspool the Department had not yet fully analyzed. The two highest-priority areas it named were Upcountry Maui and Kahaluʻu, on Oʻahu’s windward side, with about 740 cesspools.

The prioritization tool. Act 132 (2018) created the Cesspool Conversion Working Group, and the Hawaiʻi Cesspool Prioritization Tool built for it re-scored every cesspool in the state by census tract — on how many cesspools sit in the area, the soils, how close they are to drinking-water wells, streams and the shoreline, and what sits downstream of them. The tool kept the old numbers but retired the placeholder, so every cesspool now falls into one of three levels. Priority 1 is the greatest contamination hazard (red on the map), the top 25% of scores. Priority 2 is a significant hazard (orange), the next 25%. Priority 3 is a pronounced hazard (yellow), the bottom half. Statewide that is 13,821 cesspools in Priority 1, 12,367 in Priority 2 and 55,237 in Priority 3 — and about 35% of all Priority 1 cesspools are on Oʻahu.

What your level means for your timeline. The only deadline in law is still January 1, 2050, for every level. The Working Group’s final report to the 2023 Legislature recommended replacing it with a staggered schedule — Priority 1 by 2030, Priority 2 by 2035, Priority 3 by 2050 — along with conversion at point of sale and a seller’s disclosure requirement. The Legislature has not adopted that schedule; the “Do I have to convert right now?” section above covers where the proposals stand. Priority has already decided money once: the state’s 2023 pilot grant, since expired, was open only to cesspools in Priority 1 or 2 areas. So if you are in Priority 1 or 2, plan as though your deadline is earlier than 2050 and expect to be first in line for whatever help exists; if you are in Priority 3, 2050 is the date and nobody has proposed moving it.

To find your level, look your parcel up on the University of Hawaiʻi Sea Grant Cesspool Prioritization Tool, or start with our Oʻahu cesspool data, which puts 1,340 of the island’s 6,763 owner-matched cesspool parcels in the highest tier.

No. As of mid-2026 the only deadline in law is 2050, and there is no requirement to convert when you sell a home — though sellers must disclose a cesspool, and buyers increasingly factor the conversion cost into their offers.

But here is the honest picture of why leaving it until 2045 is a risky plan:

The first question a small-lot owner asks is whether a septic system is even allowed. The answer is set by the Department of Health’s wastewater rules, Hawaiʻi Administrative Rules Chapter 11-62, and they are specific:

Two things follow. A house that passes five bedrooms — a main house plus a rental counts together — needs a second system and, under the 10,000-square-foot rule, the land to put it on. And the ground has the final say: where the soil will not percolate, the water table sits high, or a drain field simply will not fit, the design moves to an aerobic treatment unit, which treats the wastewater in the tank and needs far less ground to dispose of it. The percolation test and the engineered design settle it, which is why the assessment comes before any number.

Pre-1991 lots under 10,000 square feet with a cesspool are common in older Oʻahu neighborhoods, and they are exactly the properties where “one system, no more” and the bedroom count have to be worked out before anyone quotes. Where a conventional drain field is possible, it is usually the cheaper path; where it is not, the ATU is what the rule points you to.

The $25,000 to $50,000 figure is a total, and totals are hard to plan around. Here is roughly where the money goes on a typical Oʻahu conversion. The evaluation and engineering figure is what we see on Oʻahu; the rest are the ranges reported across Hawaiʻi. All of them move with site access, soil type and how difficult the ground is — your own number comes from a site assessment.

Two things push a job toward the upper end. The first is ground: hard rock, a high water table, or steep or tight access all mean more machine time. The second is distance — long pipe runs and awkward truck access add labor to every stage. Materials and heavy equipment are imported, which is why the same work costs more here than on the mainland.

Nobody should commit to a five-figure conversion off a web page. Before any of that, we will come out, look at what you actually have, and give you a free, no-obligation estimate.

You get a straight read on your system and what the work would realistically involve — before you spend anything on engineering. Call (808) 630-9966 to set one up.

This is the part of the picture that changes most often, so here is where it stands as of mid-2026:

A typical conversion project on Oʻahu runs through six stages. End to end most take a few months — and most of that is design and permitting, not construction.

Conversion is a when, not an if — but until it happens, a maintained cesspool protects your property and keeps your household out of emergency territory. That means pumping every one to three years depending on size and use, and paying attention to the early warning signs: slow drains, gurgling plumbing, odors, or soggy ground near the cesspool.

That is the work we do every day, all over Oʻahu. We handle cesspool pumping and service now, and septic system installation, replacement and repair when you are ready to convert. When you want the job itself scoped, see cesspool conversion on Oʻahu — what the work involves, what it costs, and a free inspection to find out what your property can support.