Water from the Hutt River begins to flow underground south from Taita Gorge, then becomes pressurized under a seal of clay.

The Waiwhetu aquifer covers a wedge-shaped area of 75 km² under the Hutt Valley and Wellington Harbour, and by size is the fifth-largest in New Zealand.

[1] The harbour basin contains massive quantities of gravel washed down from the Hutt River, in some places hundreds of metres deep.

[3] Water flows down into the aquifer from a five-kilometre stretch of the Hutt River south of Taita Gorge, at the rate of 1000 litres per second.

[1] The water level in Wellington Harbour was much lower 20,000 years ago, and the ancient Hutt River used to flow down a paleochannel to the east of Matiu / Somes Island as far as the present-day Miramar Peninsula.

[13] Another pumping station was built at Buick Street in Petone in 1963 after water supply from the Korokoro Stream deteriorated.

[8] The Waterloo plant serves Hutt Central, Naenae, the Western Hills, Eastbourne, Gracefield and Petone.

[8]: 13  A 2014 report identified 13 private bores in the Hutt Valley and Petone area, five of which had consents to take 1,000 cubic metres or more of water from the aquifer each day.

[3]: 12 At the time of its sale in 2014, the Unilever soap factory in Petone had consent to take 900,000 cubic metres of water from the aquifer each year.

One is at the Dowse Art Museum in Lower Hutt, where a small park with a water feature was created in 2012,[22] and the other is Te Puna Wai Ora (Spring of Life) in Buick Street, Petone, built in 2003.

[23][10] Moore Wilson's produce store in Wellington has an artesian bore that provided water to the public.

[24] Lime is added to aquifer water coming in to the Waterloo station, to adjust its pH level so that the pipes are not damaged.

[28] In August 2016 there was a major outbreak of gastroenteritis in Havelock North caused by public water supply contamination.

It was suspected that the contamination was a result of ground disturbance caused by the Kaikōura earthquake on 14 November, but an investigation by Wellington Water did not reach a firm conclusion.

After comprehensive testing and investigation, Greater Wellington Regional Council decided to continue chlorination permanently and install UV filters at the Waterloo plant.

[28] In April 2017 the unchlorinated bore supply available to the public at Te Puna Wai Ora and the Dowse Art Museum were shut down after returning positive results.

[8][30] A new pipe system for water diversion was also installed along Knights Road, through Lower Hutt to the harbour, completed by the end of 2017.

[33] Matiu / Somes Island gets its fresh water from a bore sunk into the aquifer just off shore at the main wharf.

For example, in 1929, workers driving piles for a wharf at Point Howard pierced the aquifer, causing a large spring to form.