How 53 million gallons of raw sewage per day reaches Hawaii’s beaches — and what it means for swimmers
Unlike mainland states where contamination spreads slowly through dense soil, Hawaii’s volcanic rock is extremely porous. Cesspool effluent can travel through lava tubes and fractured basalt much faster than through typical soil — sometimes reaching the ocean in days rather than years.
Untreated human waste, pharmaceuticals, and household chemicals collect in an unlined pit. No filtration, no treatment.
Hawaii’s porous basalt allows liquid to percolate quickly into the groundwater table. Lava tubes can act as express highways for contamination.
Contaminated groundwater moves downhill through the island’s freshwater lens, mixing with the aquifer that also supplies drinking water in some areas.
Contaminated groundwater seeps invisibly through sand and reef into nearshore waters. University of Hawaii studies have measured elevated bacteria, nitrogen, and pharmaceutical compounds at SGD sites near cesspool-dense neighborhoods.
The most cesspools of any island by far. The Puna district alone has tens of thousands, built on young, extremely porous lava flows. Richardson Beach and Hilo Bay are directly affected. The 2018 Kilauea eruption destroyed some cesspools but created new groundwater contamination pathways.
Big Island Water Quality →Concentrated on the North Shore (Haleiwa, Waialua, Sunset Beach area), windward side, and rural parts of central Oʻahu. The Ala Wai watershed drains areas with significant cesspool density into Waikiki. The 2026 Nature study projects the entire Ala Wai drainage system will fail by 2050 as rising groundwater inundates infrastructure.
Concentrated in West Maui (Lahaina, Kāʻanapali area) and upcountry. The August 2023 Lahaina wildfire destroyed structures with cesspools, raising concerns about uncontrolled releases of contaminated material. A 200,000-gallon wastewater spill was reported in the area in early 2026, partially attributed to damaged infrastructure. Injection wells at the Lahaina Wastewater Reclamation Facility were already found to be contaminating nearshore waters in a landmark federal court case.
North Shore communities (Hanalei, Princeville, Kilauea) have notable cesspool density. Hanalei Bay — fed by four rivers that pass through cesspool-dense areas — has one of the highest bacteria failure rates of any monitored beach in the state. Kalapaki Beach (100% DOH failure rate in recent monitoring periods) is also affected by upstream cesspools.
Hawaii’s cesspool crisis isn’t static — it’s being amplified by climate change in three compounding ways:
As sea levels rise, the coastal water table rises with them. Cesspools that currently sit above the water table will become submerged, causing raw sewage to overflow directly into saturated soil and then rapidly into the ocean. A 2026 Nature Scientific Reports study projected that 100% of the Ala Wai watershed drainage will fail by 2050 due to groundwater inundation. Read the Ala Wai study →
Kona Low storms and atmospheric rivers are becoming more intense. Heavier rainfall raises the water table faster, pushes cesspool contamination into waterways more quickly, and overwhelms drainage systems. The March 2026 Kona Low produced record rainfall across Oʻahu. Kona Low impact guide →
Rising ocean temperatures can increase how long harmful bacteria survive in coastal waters, extending the contamination window after each rainfall event. Combined with more frequent storms and rising groundwater, this creates a compounding feedback loop.
In 2017, Hawaii became the first state to mandate the elimination of all cesspools. Act 125 requires every cesspool in the state to be upgraded to a septic system, aerobic treatment unit, or connected to a sewer line by January 1, 2050.
The math is not encouraging
With 88,000 cesspools and 24 years remaining (as of 2026), Hawaii needs to convert approximately 3,667 cesspools per year — or roughly 10 per day, every day — to meet the deadline. The conversion rate as of 2026 is far below this pace. Individual conversions cost $20,000 to $50,000 per property, with community sewer connections costing significantly more.
Priority areas under Act 125 include cesspools within 200 feet of the shoreline, perennial streams, or drinking water sources. Financial assistance is available through county programs and the state’s cesspool conversion working group, but funding is limited relative to the scale of the problem.
You can’t see cesspool contamination, but you can reduce your exposure:
Safe to Swim Hawaii aggregates DOH bacteria testing, USGS stream flow, and NWS rainfall data. Check your beach now →
Rainfall raises the water table and accelerates the flow of cesspool contamination to beaches. Wait at least 72 hours after heavy rain. Full guide →
Beaches far from streams and springs have lower cesspool contamination risk. Ko Olina Lagoons, Hapuna Beach, and Poipu Beach consistently have the cleanest water.
Brown, green, or murky water near shore — especially near stream mouths — often indicates elevated bacteria. When in doubt, don’t go in. Check active advisories →
Offshore activities avoid cesspool-affected nearshore zones. Boat-based snorkeling takes you to open-ocean reefs with pristine water quality.
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Disclaimer: Safe to Swim Hawaii aggregates data from the Hawaii Department of Health Clean Water Branch, USGS National Water Information System, EPA BEACON, NWS, and other public sources. This site does not conduct independent water testing. Always check official DOH advisories before swimming. We do not claim any beach is “safe” — we provide data to help you make informed decisions. Cesspool counts are estimates from the Hawaii Department of Health and may vary by source. Water quality can change rapidly, especially during and after storm events.
© 2026 Safe to Swim Hawaii. Data updates every 15 minutes.