83,000 cesspools. 52 million gallons per day. How Hawaiʻi's biggest pollution source affects the beaches you swim at.
A cesspool is essentially a hole in the ground that collects raw sewage. Unlike septic systems, cesspools have no treatment mechanism — waste simply seeps into the surrounding soil. In Hawaiʻi, the porous volcanic rock allows this untreated sewage to travel quickly through the ground and into nearshore ocean water.
Hawaiʻi has approximately 83,000 cesspools — the highest per-capita rate in the nation. Together, they release an estimated 52 million gallons of untreated sewage into the ground every single day. Much of this waste reaches the ocean through submarine groundwater discharge, contributing bacteria, nutrients, and pathogens to coastal waters where people swim.
Hawaiʻi's volcanic geology is the key factor. Unlike mainland soils that can filter contaminants over long distances, Hawaiʻi's porous lava rock allows sewage to travel rapidly underground. Studies have shown that waste from cesspools can reach the ocean in as little as hours to days, depending on proximity and geology.
The contamination enters the ocean as submarine groundwater discharge — fresh water seeping up through the ocean floor or flowing out along the shoreline. This creates invisible plumes of bacteria-laden water at many beaches, particularly in areas with high cesspool density near the coast.
The Waikiki area is heavily influenced by the Ala Wai Canal watershed, which drains neighborhoods with thousands of cesspools. ʻEwa Beach and surrounding West Oʻahu communities have high cesspool density. Parts of the North Shore near older residential areas also see cesspool impacts.
Kīhei and Lahaina areas have significant cesspool concentrations near the coast. Injection wells (a related issue) at the Lahaina Wastewater Reclamation Facility have been shown to discharge treated wastewater that reaches the ocean. Kamaole beaches and areas near older development are affected.
Hanalei Bay has documented water quality issues linked partly to cesspools in the Hanalei watershed. Residential areas along the coast throughout the island rely heavily on cesspools.
Hilo Bay has some of the most significant cesspool-related water quality issues in the state, with thousands of cesspools in the watershed. Kēaukaha Beach and nearby areas are frequently under advisory. The Kona coast also has cesspool concerns in developing areas.
In 2017, the Hawaiʻi State Legislature passed Act 125, mandating that all cesspools be upgraded, converted to septic systems, or connected to sewer lines by 2050. Priority conversions include cesspools within 200 feet of the ocean, streams, shoreline, or drinking water sources.
The state has established some financial assistance programs, but the conversion cost — typically $20,000 to $40,000 or more per property — remains a significant barrier for many homeowners. At the current pace of conversion, meeting the 2050 deadline will be extremely challenging.
Unlike brown water from storm runoff, cesspool contamination enters the ocean as clear groundwater. You cannot see it, smell it, or taste it. The only way to know is through bacteria testing data and DOH advisories. Beaches near older residential areas with known cesspool concentrations carry higher risk, especially after heavy rain when the water table rises and pushes more contaminated groundwater into the ocean.
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⚠️ Important Disclaimer
Safe to Swim Hawaii is an independent passion project — it is not affiliated with the Hawaii Department of Health or any government agency. Water quality ratings on this site are estimates based on publicly available testing data and geographic analysis. They are not real-time measurements and may not reflect current conditions.
Always verify current water quality conditions with the Hawaii Department of Health Clean Water Branch before entering the water. This site is for informational purposes only and should not be the sole basis for any swimming decisions.
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