Wellington City Council is due to turn on the tap from its new $3.5 million earthquake-resilient water reservoir to the city's main water supply.
The Mt Albert Reservoir holds 2.2 million litres of water, two and a half times that of its 105-year-old predecessor.
It triples the stored water for the Melrose, Southgate and Houghton Bay areas.
Mayor Celia Wade-Brown will today open a valve to connect the reservoir, which is resilient to a severe earthquake, to the main water supply.
She says almost 70 percent of Wellington's water is now in seismically strengthened reservoirs, of which more than 80 percent have automatic shut-off valves so they don't empty if the pipe network is damaged.
However she reminded households to prepare on the home front.
"Damage could occur in many places on the network and it may not be convenient to collect water from the big reservoirs.
"We encourage households to store enough water for at least seven days by installing a rainwater tank as well."
The new reservoir is underground and took 16 months to build.