No — wait 72 hours minimum. Hawaii’s 83,000 cesspools and urban runoff spike bacteria up to 500% after rain. If the water looks brown, stay out — even if no advisory has been posted. The 72-hour rule applies to every beach on every island. Which beaches recover fastest? Read on.
Do not swim in Hawaii for at least 72 hours after heavy rain. Stormwater washes sewage from Hawaii's 83,000 cesspools, animal waste, and urban runoff into the ocean through streams and storm drains. Studies show bacteria levels spike up to 500% above safe limits after storms — and the water can look completely clear while still being dangerous. The DOH recommends waiting until the beach has had full sunshine for at least three days before returning to the water.
If the water looks brown: stay out, no matter what. Brown color means runoff is still actively flowing in. Some beaches stay contaminated for 5+ days — especially near stream mouths like Kailua Beach, Waikiki (Ala Wai Canal), and Kalapaki on Kauaʻi. Leeward beaches without streams (Wailea, Ko Olina, Hapuna) recover fastest. See the full list below.
Hawaii has approximately 83,000 cesspools that discharge an estimated 52 million gallons of undertreated sewage into the ground and coastal waters every day. When it rains, this sewage — along with animal waste, agricultural chemicals, fertilizers, motor oil, and urban debris — gets flushed through streams and storm drains directly into the ocean.
The result is the “brown water” that gives Hawaii’s brown water advisories their name. But the visible discoloration is mostly dirt and sediment. The real danger is invisible: enterococcus and other fecal indicator bacteria that can cause gastrointestinal illness, skin rashes, ear infections, eye infections, and wound infections.
The Hawaii DOH pauses bacteria testing at beaches during brown water advisories. This means the highest-risk periods have the least data. The DOH also only tests 57 of Hawaii’s 250+ beaches on a weekly basis — most beaches are never tested at all.
The Surfrider Foundation conducted a 3-year study tracking over 10,000 surf sessions in San Diego. They found that illness rates were highest during rain and the first day after, then declined steadily, reaching near-baseline levels after 72 hours. That research is the basis for the widely-cited 72-hour rule.
However, a UCLA study analyzing 7 years of water quality data found that bacteria levels can remain elevated for up to 5 days near storm drains and creek outlets. For beaches with these features, a longer wait may be appropriate.
Open-ocean beaches on dry coasts, away from streams: 48–72 hours is typically sufficient. These beaches have strong ocean flushing and fewer contamination sources.
Beaches near stream mouths or storm drains: Wait the full 72 hours minimum, or longer if the rain was heavy. Stream-adjacent beaches receive the most concentrated runoff.
Enclosed bays or breakwater-protected beaches: Wait 72 hours to 5 days. Limited water circulation means contaminants disperse more slowly. Examples: Ala Moana, Kahalu’u Beach Park.
Freshwater streams and ponds: The DOH warns against entering freshwater after any rain due to leptospirosis risk, a serious bacterial infection that can be fatal. This applies to waterfall pools, river crossings, and any standing freshwater.
Hawaii has two seasons, not four. The wet season runs from roughly November through March, with December through February typically being the rainiest months. The dry season runs from May through October. The transition months of April and October can go either way.
The majority of brown water advisories and bacteria exceedances happen during wet season. But rain in Hawaii is extremely localized — it can be pouring on one side of an island while the other side is sunny and dry.
Every Hawaiian island has a wet side (windward — north and east, facing the trade winds) and a dry side (leeward — south and west, sheltered by the mountains). The rainfall difference is enormous: Hilo on the Big Island’s windward coast gets 10 to 40 times more rain than the Kona resort coast just 50 miles away.
This means choosing the right coast matters more than choosing the right month. A leeward beach during wet season can be drier and cleaner than a windward beach during dry season.
The safest beaches after rain share three characteristics: they’re on dry leeward coasts, they have no stream mouths nearby, and they have strong ocean circulation.
These beaches sit near stream mouths, have chronic cesspool contamination, or sit in enclosed bays where runoff lingers.
Best months: May–October. The south shore (Waikiki) is drier year-round but Ala Moana has chronic issues from the Ala Wai Canal regardless of season. The North Shore gets heavy winter rain and surf. Ko Olina’s man-made lagoons self-clean via ocean currents and hold up well even during wet season.
Best months: May–October. South Maui (Wailea, Makena) is the driest coast and has the cleanest water year-round. West Maui (Ka’anapali, Kapalua) gets more winter rain but is still significantly drier than east Maui. Hanakaoo near Ka’anapali has shown worsening bacteria trends regardless of season.
Best months: May–September. Kaua’i gets more rain than any other island. The south shore (Poipu) is the driest and most reliable for clean water. Hanalei Bay on the north shore has been DOH-impaired since 2004 — wet season makes it worse, but the underlying cesspool problem exists year-round. Kalapaki near Lihue has failed bacteria tests 100% of the time since 2016.
Best months: Any — the Kona coast is dry year-round. Hapuna Beach on the Kohala Coast is one of the cleanest beaches in the state in any month. The Hilo/east side is one of the wettest places on earth and should be avoided for swimming after any rain. Kahalu’u in Kona has confirmed cesspool contamination that worsens after rain.
Hawaii DOH Clean Water Branch — The official source for active brown water advisories, beach advisories, and sewage spill notifications. Visit the DOH CWB website →
Safe to Swim Hawaii — This site pulls DOH advisory data every 15 minutes and combines it with historical bacteria testing data and risk ratings for 100+ beaches and 25+ hotels across all islands. Check your beach →
Visual inspection — If the water looks brown, murky, or discolored, don’t go in. This applies even when no advisory has been issued. If you can see a stream flowing brown water into the ocean, stay well away from the mixing zone.
Recovery time depends on three things: how much rain fell, how many streams drain into the beach, and how well the ocean flushes the area. Leeward beaches with no stream outlets can clear in a day. Windward beaches near rivers can take almost a week. This table shows typical recovery times after moderate-to-heavy rain (1–3 inches in 24 hours).
| Area | Recovery | Why |
|---|---|---|
| North Shore O’ahu | 3–5 days | Waimea River and Haleiwa stream carry heavy upland runoff. Waimea Bay sits right at a river mouth. |
| Waikiki | 2–4 days | The Ala Wai Canal collects runoff from the entire valley behind Waikiki and dumps it at the west end of the beach. |
| Kailua | 2–3 days | Kailua Beach receives runoff from Kawainui Marsh, one of the largest wetlands in Hawaii. Stream outlets at both ends of the beach. |
| Ko Olina | 1 day | No streams. Man-made lagoons flush via ocean channels. Dry leeward coast gets minimal rain. |
| Maui South Shore Wailea / Kihei |
1–2 days | Minimal streams on the driest coast in Hawaii. Wailea recovers fast with strong ocean flushing. |
| Maui West Side Ka’anapali / Lahaina |
2–3 days | Multiple stream outlets along the coast. Hanakaoo has shown chronic bacteria issues. Kapalua Bay is more sheltered and clears faster. |
| Kaua’i North Shore Hanalei / Princeville |
3–5 days | One of the wettest places on earth. Hanalei Bay has 4 streams and 360+ cesspools. DOH-impaired since 2004. |
| Kaua’i South Shore Poipu |
1–2 days | Poipu sits on the dry leeward coast with minimal stream influence and strong ocean circulation. |
| Big Island Kohala Coast Hapuna / Kua Bay |
1 day | Dry side, almost no runoff. Hapuna and Kua Bay are among the cleanest beaches in the state year-round. |
| Big Island Hilo Side | 3–5 days | Hilo gets 130+ inches of rain per year. Constant streams, rivers, and waterfalls feed the coast. Avoid swimming after any rain on this side. |
These times assume the rain has fully stopped and sunshine has returned. If it’s still drizzling or overcast, the clock hasn’t started. UV light is one of the main factors that kills bacteria in shallow coastal water.
The 72-hour rule is the most widely cited guideline for swimming after rain in Hawaii. It comes from a Surfrider Foundation study that tracked illness rates among surfers in San Diego over three years. But that study measured average conditions at average beaches after moderate rain. Hawaii has unique factors that can push the safe window well beyond three days.
A Kona low is a subtropical weather system that reverses normal wind patterns and dumps heavy rain on the dry leeward coasts that normally stay clean. Unlike typical trade-wind showers, Kona lows can drop several inches across an entire island over multiple days. When that happens, even beaches that rarely see contamination — like Wailea and Ko Olina — can have elevated bacteria levels. After a multi-day storm event, beaches near stream mouths can stay contaminated for 5 to 7 days.
The specific bacteria the DOH tests for is enterococci — fecal indicator bacteria found in the intestines of humans and animals. After rain, enterococci enters the ocean through two main pathways: sewage overflow from Hawaii’s approximately 88,000 cesspools, and animal waste washed off agricultural land, urban areas, and forested watersheds. Enterococci can cause gastrointestinal illness, skin infections, ear infections, and eye infections. Children, elderly visitors, and anyone with open wounds are at highest risk.
Hawaii has roughly 88,000 cesspools — more than any other U.S. state. These are unlined underground pits that receive raw sewage and let it seep into the ground and groundwater. During heavy rain, the water table rises and cesspools overflow, pushing untreated human waste directly into streams and coastal waters. The state legislature passed Act 125 in 2017 requiring all cesspools to be converted or replaced by 2050, but progress has been slow. Until then, every heavy rain event is a sewage event.
Here is the part that frustrates longtime residents most: the Hawaii DOH pauses water quality testing during brown water advisories. That means during the highest-risk period — right after a big storm — there is literally no official bacteria data. The DOH only tests 57 of Hawaii’s 250+ beaches, and only on a weekly schedule. So when you need data the most, you get none. That’s one of the reasons we built Safe to Swim Hawaii — to fill in the gaps with historical data and risk ratings when the official system goes quiet.
72 hours is the minimum for moderate rain at a well-flushed beach. After a Kona low, tropical storm, or multi-day rain event, extend that to 5–7 days — especially at beaches near stream mouths. And if the water looks brown at any point, the clock resets.
People who live in Hawaii and swim year-round don’t just follow a blanket rule. They make decisions based on specific conditions. Here’s the decision-making process most experienced ocean swimmers use.
Rain in the mountains above a beach matters more than rain at the beach itself. The watershed is what feeds the streams. It can be sunny at Waikiki while it’s pouring in the Ko’olau mountains behind it — and that mountain rain will flush right down the Ala Wai Canal to the beach hours later.
This is the simplest and most reliable test. If the water has any brown tint, visible sediment plumes, or debris floating in it, stay out. It doesn’t matter if no advisory has been posted. Brown water = active runoff = bacteria. Clear blue water is the green light.
Trade-wind showers hit the windward (north/east) side. If it just rained, drive to the leeward (south/west) coast. On O’ahu that means Ko Olina instead of Kailua. On Maui, Wailea instead of Pa’ia. On the Big Island, Kona instead of Hilo. On Kaua’i, Poipu instead of Hanalei.
Open-ocean beaches with strong currents and wave action flush contamination much faster than enclosed bays, lagoons, or breakwater-protected beaches. Ala Moana is a classic example — the reef and breakwater trap runoff inside the swimming area. An open-coast beach like Hapuna exchanges water with the open ocean constantly.
If it rained in the last few days and you need a beach, these are your best bets on each island. They share the same traits: leeward coast, no stream mouths, and good ocean flushing. Recovery times listed are for moderate rain (1–2 inches).
During a Kona low, even these “safe” beaches can be affected because the rain hits the normally dry leeward coasts directly. After a Kona low, add 1–2 extra days to these recovery estimates and do a visual check before getting in.
100+ beaches and 25+ hotels across all 6 islands
⚠️ 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. “No DOH Alerts” means no advisory is currently posted — it does not mean the water was tested and found safe. DOH only monitors a fraction of Hawaii’s beaches, and some areas have no regular testing at all.
Always verify current water quality conditions with the Hawaii Department of Health Clean Water Branch before entering the water.
When in doubt, don’t go out. 🤙