Division of Collection System Maintenance
Preventing Sewer Spills: Our Multi-Faceted Approach
The majority of sewer spills across Oʻahu are caused by grease buildup, invasive tree roots, and debris. Other contributing factors include broken or sagging pipes, as well as heavy rain events that overload the system.
To tackle these issues, the Department of Environmental Services (ENV) has an active Preventive Maintenance (PM) program in place. This comprehensive effort targets grease and roots within the city’s sewer lines using a combination of mechanical, chemical, and educational strategies.
Our Collection System Maintenance crews use high-powered Vactor trucks to flush out grease from sewer lines and deploy both mechanical and chemical tools to remove and prevent root intrusion. Sharp cutting tools are inserted into pipes to clear away roots, followed by a foaming herbicide that discourages regrowth for 6 to 12 months.
To detect system vulnerabilities, ENV also conducts smoke testing—a method that pushes non-toxic smoke through the sewer lines to reveal cracks, illegal connections, or breaks where water or debris can enter. If not properly managed, these areas allow rainwater to infiltrate the sewer lines and contribute to costly and disruptive spills.
On the private side, ENV’s Environmental Quality Division—specifically the Regulatory Control Branch—monitors commercial and residential sources of grease. This includes restaurant grease traps, household drains, and other points where fats, oils, and grease (FOG) may enter the system.
The FOG Program supports this work through routine inspections, investigations, enforcement actions, and proactive education to help the public understand the impact of improper grease disposal—and how to prevent it.
Together, these efforts help keep our sewer system flowing and our environment protected.
Keeping Rainwater Out of the Sewer System
The city’s Department of Environmental Services (ENV) is teaming up with communities across Oʻahu to prevent rainwater from entering the sewer system—one neighborhood at a time.
Using a method called smoke testing, ENV crews identify leaks, broken or aging pipes, and illegal connections on private properties that allow stormwater to flow into the city’s sewer lines. If smoke can escape, that means water can enter.
So far, more than 10,000 private properties have been tested—and about 8% have shown signs of inflow issues. These include missing or damaged cleanout caps, cracked pipes, or improper drainage connections. The good news? Most of these problems are quick and affordable to fix. In fact, the most common issue—a missing cleanout cap—can be replaced for just around $7 at any local hardware store.
While each small leak may not seem like a big deal, the impact adds up. Studies show that roughly half of the water treated at our wastewater plants comes from unwanted residential inflow, especially during heavy rain.
That’s why ENV is committed to identifying these problem areas island-wide and notifying property owners about what needs to be fixed. We prioritize neighborhoods with frequent wet weather flooding. Residents will receive a letter from the city two weeks before testing starts, followed by a door hanger one week before crews arrive.
Together, we can protect our sewer system, reduce overflows, and keep our environment clean.
What Is Smoke Testing—And Why It Matters
To protect our island’s sewer system from overflow, the Department of Environmental Services (ENV) uses a method called smoke testing to find where unwanted rainwater might be sneaking into the city’s sewer lines.
Here’s how it works:
A special machine pumps non-toxic, odorless smoke into a manhole on the street. The smoke travels through the city’s sewer main and into the smaller, spider-like plumbing lines that branch off into homes. If everything is in good shape, the smoke simply escapes through the vent pipes on your roof—just as it should.
But if smoke pours out of a rain gutter, downspout, or yard drain, it’s a red flag that stormwater is being misdirected into the sewer system instead of into storm drains or the ground.
Smoke coming from a cleanout pipe in the yard might mean there’s a missing or broken cap—an issue that’s usually cheap and easy to fix.
What Happens Next?
During testing, ENV crews document results using cameras and take photos for records. If a problem is found on your property, you’ll receive a letter in the mail detailing what needs to be fixed.
Simple fixes like replacing a cleanout cap or redirecting a downspout are low-cost and must be handled promptly by the homeowner.
For more complex repairs, such as broken underground pipes, scheduling and financial responsibility may be discussed with the city. In some cases, property owners may be required to cover the cost.
Continued noncompliance may result in fines.
Why This Matters
Most homeowners are surprised—and grateful—to learn more about how their plumbing works. Many are also shocked to find out that around 50% of the excess water entering the sewer system during heavy rains comes from private property. That statistic has been confirmed by national studies and local testing here on Oʻahu.
Too much stormwater in the sewer system can lead to spills, backups, and overflows—posing risks to both public health and the environment. Fixing the problem property by property is the most cost-effective solution. Without your help, the alternative would be building larger sewer lines, storage tanks, or treatment plant upgrades—massive infrastructure projects that would cost taxpayers millions.
By working together, we can keep our wastewater system flowing properly and protect our island’s natural resources. Smoke testing is just one part of that mission—but it starts at home.
Help Prevent Sewer Spills at Home
During heavy rains, about half of the excess water entering Oʻahu’s sewer system comes from private properties—not the streets. This unwanted inflow can overwhelm the system and lead directly to sewage spills in our communities.
The good news? Small actions at home can make a big difference.
What You Can Do:
✔ Check your cleanout cap
A missing or damaged cap is one of the most common (and preventable) problems.
You can pick one up at most hardware stores—just be sure to measure for the right size.
City sewer crews often carry extras—if you see them working in your neighborhood, feel free to ask!
You can also have a licensed plumber install or repair the cap.
✔ Redirect your rainwater
Make sure gutters and downspouts drain into your yard or a storm drain—not the sewer system.
Remove any yard drains connected to the sewer, and properly cap the pipe with a cleanout cap.
✘ Never remove cleanout caps during heavy rain
Doing so allows stormwater, debris, and even pests like rats to enter the system, increasing the risk of overflows.
✔ Keep an eye on tree roots
Roots can penetrate the lateral pipe that connects your home to the city’s sewer main. If you notice slow drainage or backups, roots may be the cause.
Know Your Role
By city ordinance, it is illegal to discharge stormwater into the sewer system, and violations may result in fines.
Homeowners are responsible for maintaining their own sewer laterals (the pipe between your house and the city’s main line).
The city is responsible for public sewer mains and manholes.
By doing your part, you help protect our island’s wastewater system—and the environment we all share.
Follow the Flush
During heavy rains, half of the extra water entering the sewer system comes from private property. Excess water in the collection system leads directly to sewage spills.
Here’s how you can help:
- Is your cleanout cap missing or damaged?
- City sewer maintenance workers often carry extra caps with them. Ask for one.
- Have a private licensed plumber repair the fault.
- Purchase and install the cleanout cap yourself (measure size first).
Drain rain gutters into a storm drain or directly onto the grass. Remove yard drains and cap the sewer pipe with a cleanout cap.
DO NOT REMOVE cleanout caps during heavy rains, allowing water, rats or other objects to enter the collection system.
Watch for tree roots penetrating the lateral in your yard or driveway.
Discharging storm water into the sewer system violates a City Sewer Ordinance. A fine may be assessed.
Residential sewer lines are the responsibility of the homeowner. Sewer mains and manhole problems are the responsibility of the City.
How Wastewater Spills Happen
On Oahu, as in other developed coastal and island areas around the world, heavy rains and spills go hand-in-hand.
ENV crews are well-trained, well-equipped and highly motivated. They are part of our community and care about it, as you do.
Whatever the cause—heavy rains, a ruptured pipe, old or malfunctioning equipment, the protocol is generally the same.
Warning signs are posted immediately at potentially affected beaches and streams to alert people to keep out of near shore waters. We collect water samples and test for harmful bacteria. We bring in 3,000-gallon capacity pump trucks to suck up the spills on land. Other team members find the problem and fix it, then help homeowners deal with problems on private property.
After a spill, lab specialists continue collecting samples for testing until Oahu’s oceans and streams are cleared. We process the results within 24 hours and deliver them to the state Department of Health (DOH) for review. Warning signs remain until we are certain water quality is safe. (Sadly, warning signs are often stolen as quickly as they are put up). DOH decides when the waters meet state and federal clean water requirements and are safe for recreation.
Wastewater spills are bound to occur in a heavily populated island community such as Oahu. The wastewater system is constantly being repaired and upgraded to reduce the frequency and severity of spills.