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Water Main Breaks The Underground Truth

Water – more than electricity or gas – is the most infrastructure-intensive utility there is because water requires pumping, treatment, storage and transport through pipes over long distances. Water utilities are paying attention to their infrastructure now more than ever because it is reaching or passing its useful life. Just as you need to maintain, repair and periodically replace your roof so it continues to protect you from the rain, the Board of Water Supply (BWS) needs to do the same for Oahu's water facilities and infrastructure. It is a large undertaking.

bws facilities and infrastructure

BWS has one of the largest water facilities and infrastructure system in the country.

Why Do Breaks Occur?

The BWS collects information on main breaks to help determine the cause of failure. This information is used to identify what we might do to reduce breaks in the future, for example, by changing pipe materials, design specifications, construction methods, or other protective measures. Unfortunately, because of the sudden release of water when a break occurs, much of the evidence is often destroyed, so this is a very complicated task. 

As part of condition assessments done for the Water Master Plan, the BWS has identified certain pipe materials and corrosion as the main reasons why pipes break on Oahu. Cast iron pipes were the industry standard for water pipelines starting in the late 1940s. Now among our oldest, these cast iron pipes are more prone to corrosion. Other factors that can reduce the useful life of pipe are smaller diameters, higher water pressures, corrosive soils, and construction quality.

By understanding these underlying causes, BWS can proactively replace pipes to reduce the risk of future breaks. The BWS plans to increase annual pipeline replacement to 21 miles per year within the next 10 years. Currently, approximately 6 miles of pipeline are replaced annually.

predicted number of main breaks
(Source: Water Master Plan Quarterly Update, November 2017)

Investing in Maintenance & Prevention

Although Oahu experiences far fewer main breaks than the national average, the resulting inconvenience, damage, and cost means we must act quickly. This is what the Board of Water Supply (BWS) is doing to prevent future main breaks:

  • Replacing portions of the system that are most vulnerable to breaks and most critical to service dependability.
  • Extending the life of water mains in areas of highest corrosion potential.
  • Conducting forensic analysis to determine the primary causes of main breaks and identify changes to design, construction, and operation.
  • Pinpointing small cracks or holes for repair.
  • Encouraging customers to reduce water use and adjusting operations to increase efficiency, which reduces water being pumped through the system and means less stress on pipelines.
  • Developed a 30-year Water Master Plan to identify and prioritize long-term improvements.
  • Developed a 30-year Capital Improvement Program (CIP).

BWS Water Main Break Repair (PDF)

When a main breaks, the Board of Water Supply’s top priority is to protect public health and safety, while minimizing water loss and the impact on the public. Repairs are complex and require considerable care and time. Our crews work to restore service as quickly as possible. Here is a quick overview of what they do:

stop water loss


Upon learning of a main break, we go to the site to close the necessary valves to stop water loss and isolate the broken section from the rest of the main. We close valves gradually to protect the rest of the system from abrupt changes in pressure and flow. initially, the water outage may be more widespread until the break is isolated. Then once we start repairs, we try to keep water flowing to the rest of the system to minimize impact to our customers.


Prior to the repair, utilities with buried conduits near the main are notified to mark their lines so we can avoid damaging them.

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repair the water main


We set up a water wagon, or a spigot on a nearby hydrant, for customers who lose water service during repair. If a break affects many people or a vital traffic route, we alert media and the public via HNL.info, social media, or our website. If the break has a significant impact on traffic, we work with other City and State agencies on mitigation plans. When appropriate, we arrange with the police for traffic control.

Sign-up to receive free HNL.Info email, text messages or push notifications from the City & County of Honolulu about major water main breaks, traffic situations, upcoming events and other advisories. Sign up online or download the app now.

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restore water service


We clear debris, set up safety equipment, excavate the main (most pipes are 3 to 10 feet underground), and pump out excess water around it. Excavating can be prolonged if there are other buried utilities close by. Once the main is unearthed, we can determine the extent of damage and make repair. Often, we need to replace the damaged section.


Once repair is done, we test the new pipe to ensure it is fit for service and disinfect it to protect public health and water quality. Next, we open a nearby hydrant to flush air and debris out of the pipe. Then, we reconnect customer lines to the main and carefully re-open the valves so that water will again flow through the main and build up pressure to normal levels.

restore the roadway


Last, we refill the repair trench and prepare the road for patching. We install a temporary patch to cover the excavated area until a pavement contractor can put in a permanent one.

To report a possible water main break day or night, call (808) 748-5000, ext. 1

Updated: 01/27/2022