Published September 3, 2026
Start with the water bill. If your Board of Water Supply bill carries a City sewer charge, the house is on the county sewer. If it does not, the house has its own system in the ground — a cesspool or a septic tank — and the yard, the closing documents and the state’s records will tell you which. Or we open it and tell you; the inspection is free.
It matters more than it used to. Hawaiʻi’s Act 125 requires every cesspool in the state — roughly 88,000, more than 11,000 of them on Oʻahu, per the Department of Health — to be upgraded, converted or connected to a sewer by January 1, 2050. A septic tank is not a cesspool, and a sewer connection is the finish line. So “which one do I have” is the first question, and every decision after it depends on the answer.
The water bill
On Oʻahu, sewer service is billed by the City and County’s Department of Environmental Services, and its charge rides on the Board of Water Supply bill. If there is a sewer line on that bill, you are connected. If there is not, you are not.
The charge has two parts — a monthly base charge, and a usage charge based on the water the meter records, with a discount on the usage portion if you have no separate irrigation meter. For this question the amounts do not matter; what matters is whether that sewer line appears on the bill at all.
The yard
If there is no sewer charge, walk the property.
A cesspool is a pit. There is usually a single lid — often a round concrete cover, sometimes a square one, sometimes nothing visible at all because it was buried decades ago — and there is no drain field, because the pit does the disposing. Cesspools were the standard on Oʻahu for a long time and were only banned for new construction in 2016, so an older home outside the sewered neighborhoods is a cesspool until proven otherwise.
A septic tank has two lids, one over the inlet and one over the outlet, sometimes raised to grade on risers. Downstream of it there is a drain field: a stretch of lawn that stays a little greener or a little softer than the rest, sometimes with a small distribution box between the tank and the field. If you can find two lids and a strip of suspiciously healthy grass, it is septic.
An aerobic treatment unit looks like a septic system with electricity. There is a control panel on an exterior wall with an alarm light, and a blower you can hear running. If your house has one of those, you have an ATU, and it needs power and a service schedule.
A sewer connection shows up as a cleanout — a capped pipe near the property line or the house — and nothing else. No tank, no lids, no field.
Lids get buried under lawns, lanais and driveways, so not finding one proves nothing. Finding one is what an inspection is for.
The records
Three places keep the answer on paper.
Your closing documents. Hawaiʻi sellers must disclose a cesspool, so if you bought recently, the disclosure form or a past inspection report names the system.
The Department of Health. The Wastewater Branch keeps records of individual wastewater systems, and it is the agency that permitted whatever was installed legally.
The Hawaiʻi Cesspool Prioritization Tool. The University of Hawaiʻi and the Department of Health map every known cesspool parcel in the state and assign it a priority level. If your parcel is on that map, you have a cesspool. We built our Oʻahu cesspool data page from the same source, matched to county ownership records — 6,763 parcels on this island, 1,340 of them in the highest tier.
What each one means under the 2050 law
Cesspool. It has to go. The law says January 1, 2050; the state’s Cesspool Conversion Working Group recommended 2030 for Priority 1 areas and 2035 for Priority 2, and the Legislature has not adopted that schedule yet. Your priority level tells you how much of a margin to expect. The Hawaiʻi cesspool conversion guide covers the three ways out and what they cost.
Septic. Act 125 is a cesspool law. A permitted septic system is not a cesspool, so the 2050 requirement does not apply to it. What a septic system has instead is a clock of its own — the tank needs pumping on a schedule, and the drain field has a working life. Keep it pumped and it keeps working.
Sewer. You are done, and you pay for it monthly.
What to do with the answer
If it is a cesspool, read the conversion guide, check your priority level, and get the free assessment before you decide anything — cesspool conversion is the job, and the number comes from your lot, not from a page. Small lots have a sizing rule to clear first.
If it is a septic tank, find out when it was last pumped. If nobody knows, get it pumped and measured once, and the interval stops being a guess.
If you cannot tell, call (808) 630-9966. A septic and cesspool inspection locates the system, opens it, and tells you what you have and what condition it is in — which is the one thing every buyer, seller and owner on this island should know before 2050 gets any closer.