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Published 17/03/2020

On-site and mobile generators deployed to keep water network flowing during power outage

Following the major power outage in the region on Thursday morning, Wellington Water implemented its emergency response procedures, activating on-site and mobile generators to ensure the water network continued to function until power was restored.

As a precaution, customers were immediately advised to limit water usage, including toilet flushing, to minimise demand on the network until the extent of the electricity interruption was better understood. 

Drinking water supply has good resilience in the event of a power outage, as delivery from reservoirs to homes and businesses is gravity-driven. Powered pumps transfer water from treatment plants to refill reservoirs, and these were managed using generators as required.

Wellington Water’s priority during the power outage was management of the wastewater network in the affected area. An interruption of power to the network’s treatment plants and pumping stations can cause a build-up of wastewater entering the network from users. Once the storage capacity of those facilities is exceeded, the system manages excess wastewater via constructed overflow points into the ocean or other waterways. This ‘relief valve’ approach is a legacy from an earlier era of sewer system design, and is common worldwide.

Wellington Water’s deployment of on-site and mobile generators was successful in ensuring the wastewater network continued to function without mains power, without any overflows experienced from among more than 200 emergency overflow points in the network.

One short overflow of fully treated wastewater occurred at the Seaview Wastewater Treatment Plant, as the facility switched back to mains from generator power. Signage has been put up in the area and water quality testing is being undertaken at the Waiwhetu Stream. While that facility was on generator power, essential systems were prioritised, meaning the wastewater that was being pumped to the normal outflow point into Cook Strait at Bluff Point was partially treated during that time, with no UV disinfection.

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