Question 1

Which Hawaii island has the best water quality?

Accepted Answer

The Big Island and Maui generally have the fewest bacteria advisories relative to their beach count. The Big Island's newer lava rock coastlines and relatively lower development density contribute to cleaner water at many spots. O'ahu has the most beaches and the most DOH advisories in absolute numbers, largely due to dense urban development, aging cesspools, and higher recreational use. Kaua'i has highly variable water quality — remote north shore beaches are pristine, while streams draining agricultural land can affect some spots.

Question 2

Why does O'ahu have more water quality advisories than other islands?

Accepted Answer

O'ahu has more advisories because it has more population, more development, more monitored beaches, and more frequent testing. The island has tens of thousands of cesspools that can contaminate groundwater and nearshore ocean water, particularly after heavy rain. Urban runoff from Honolulu and other developed areas also contributes. More testing means more advisories are caught and posted compared to less-monitored islands.

Question 3

Is Kaua'i water quality good for swimming?

Accepted Answer

Kaua'i has a split personality for water quality. The north and south shores have many excellent, clean beaches like Hanalei Bay and Po'ipu. However, Kaua'i's heavy rainfall and agricultural land use mean that stream mouths and low-lying coastal areas can have elevated bacteria counts after rain. The island receives the most rainfall of any Hawaiian island, which means runoff events are more frequent. Always apply the 72-hour rain rule on Kaua'i.

Question 4

What affects water quality on Maui?

Accepted Answer

Maui's water quality is affected primarily by stream and drainage runoff after rain, aging cesspools in upcountry and older coastal communities, and agricultural land use in Central Maui. The west side resort corridor (Ka'anapali, Napili, Kapalua) generally has good water quality due to reef protection and lower runoff risk. South Maui beaches like Wailea and Makena tend to have excellent water quality. Windward Maui beaches (Paia, Ho'okipa) can have elevated bacteria after heavy rainfall.

Question 5

Does the Big Island have bacteria problems at beaches?

Accepted Answer

The Big Island has relatively few bacteria advisories at ocean beaches compared to O'ahu. The island's newer volcanic coastlines, lower population density, and limited development near many beaches contribute to generally good water quality. However, some areas — particularly around Hilo Bay and coastal spots near stream mouths — can show elevated bacteria after heavy rain. The Hilo side receives enormous rainfall and runoff from forested slopes. West coast Kohala beaches are consistently among the cleanest.

ISLAND	OVERALL RISK	AFTER RAIN	MONITORING
Oʻahu	Moderate	High Risk	Most Frequent
Maui	Low-Mod	Moderate	Regular
Kauaʻi	Variable	High Risk	Regular
Big Island	Low	Low-Mod	Less Frequent