Water supply and sanitation in the Wellington region

The supply of reticulated drinking water is regulated under the Health Act, and suppliers are registered and subject to a testing regime. The registered water suppliers for the Greater Wellington region are listed in annual drinking water quality reports published by the Ministry of Health.[6]

This table omits several small supplies serving populations less than 1,000.

Water supply for the Wellington metropolitan area comes from three sources:[7]

• Hutt River
• Wainuiomata and Orongorongo rivers
• Waiwhetu aquifer

There are times each year, particularly during summer months, where the total demand is greater than can be supplied from these sources. There are two large storage lakes that can be used to supplement the supply during these periods.

Weir and water supply intake on Hutt River at Kaitoke

The Hutt river water supply catchment covers almost 9,000 hectares of bush-clad mountains and valleys at the southern edge of the Tararua Forest Park and adjoining the Kaitoke Regional Park. Rainwater from tributary streams flows into the Hutt River and is intercepted at a weir at Kaitoke, north of Upper Hutt. The water is then strained to remove sticks, leaves and silt, and piped through tunnels to the Te Mārua Water Treatment Plant. Up to 150 million litres of water per day may be diverted from the Hutt River, provided an adequate flow is maintained downstream of the weir. The Hutt water supply catchment provides about 40 percent of the water used in the Wellington metropolitan area each year.[7]

Upper Macaskill lake

There are two large storage lakes at Te Mārua – the Macaskill Lakes. These lakes are filled from the Hutt River intake when the water is clean and there is sufficient flow available. Stored water is pumped from the lakes into the treatment plant when there is not enough water in the river to meet public demand. The storage lakes are also used to meet demand when the river is too dirty – after heavy rainfall – or when it is in flood and the intake is closed to prevent rocks and gravel from entering the intake pipes.

The Macaskill Lakes are 17.3 metres deep and have a combined usable capacity of approximately 3,350 million litres, or enough to meet average water use for around 23 days.[7]

Building the lakes was first proposed in 1975. The construction of the two lakes proved difficult because of weather and on-site conditions, resulting in cost increases and litigation. There were also problems with leaks after completion, leading to further litigation.[8]

The Wainuiomata/Orongorongo water supply catchment area lies within the Remutaka Ranges to the east of Wainuiomata. The collection area covers 7,600 hectares. Five low dams (weirs) with intake pipes provide water from the rivers to the Wainuiomata Water Treatment Plant. These catchment areas provide approximately 20% of the water used in the Wellington metropolitan area each year.[7]

The Te Puna Wai Ora fountain flows with water from the Waiwhetu aquifer

The Waiwhetu artesian aquifer is a zone of water-retaining sand, gravel and boulders beneath the Hutt Valley. Water from the Hutt River starts to flow underground around Taita Gorge. From Melling southwards, the water becomes naturally pressurised beneath a layer of hard clay. This pressurised zone, the Waiwhetu artesian aquifer, stretches as far south as the harbour. It is estimated to be up to 70 metres thick at its western edge against the Wellington fault line, and 20 metres thick at the eastern edge of the harbour. The pressure in the aquifer has resulted in several fresh water springs in the harbour floor.

Water takes more than 12 months to pass through the aquifer to wells where it is extracted for distribution via the water network. Extraction is monitored and controlled to minimise the risk of saline intrusion. The Waiwhetu aquifer provides around 40 percent of the annual water supply.[7]

The Te Puna Wai Ora (Spring of Life) in Buick Street, Petone provides untreated water from the aquifer free to the public.[9][10]

The water sources for the South Wairarapa District Council area are the Waiohine catchment for Featherston, the Kuratawhiti Street bore for Greytown residents, and the Herricks bore field for users in Martinborough.[11]

Water supplies for the Kapiti Coast region are sourced from combination of bores and surface water from the Waikanae River. [12]

Water supply for the Carterton district comes from the Kaipatangata Stream and two underground bores.[13]

Masterton's drinking water is sourced from the Waingawa River, about 10 km west of Masterton.[14]

Sand trap and strainer house for water supply intake at Kaitoke

The reticulated water supply to the Wellington metropolitan area is all chlorinated. [15]Drinking water in Lower Hutt, Porirua, Upper Hutt and Wellington city is also fluoridated. The only exceptions are Petone and Korokoro. These suburbs historically had an unfluoridated water supply and this has continued following a public survey in 2000.[16]

There are four water treatment plants located in the Hutt Valley (Te Mārua, Waterloo, Gear Island and Wainuiomata). These plants supply water for use in Upper Hutt, Lower Hutt, Porirua and Wellington cities.[17] The treatment processes at the four treatment plants differ based on the characteristics of the incoming water.

At the Te Mārua water treatment plant, the main treatment processes are:[18]

• Straining
• Coagulation and flocculation
• Sedimentation
• Filtration
• Chlorination
• pH adjustment
• Fluoridation

The Gear Island and Waterloo plants both treat water that is drawn from the Waiwhetu aquifer.

The 2018/19 National Performance Review published by Water New Zealand compares the average pipeline age and condition across water supply networks. The data for the Wellington water supply network shows that 20% of the pipelines are in poor or very poor condition. The Wellington network ranks the worst on this measure out of the six large supply networks nationwide.[19] The review also includes average pipeline age. The Wellington network has an average age of 43 years, and ranks as the second oldest of the six large supply networks.[20]

During a prolonged dry spell in November 2017, Wellington Water reported that weekend consumption in the Wellington metropolitan area reached 171 million litres for the day – around 30 million litres more than a typical day, and the highest November daily consumption in five years. Wellington Water called on consumers to cut back on their water use, and make sure they observe garden watering restrictions.[21]

A National Performance Review published by Water New Zealand for the 2019 financial year showed that daily residential consumption in the Wellington metropolitan region was about 226 litres per person. By way of comparison, daily residential water use in Auckland and Tauranga was significantly lower at about 156 and 189 litres per person respectively. Both Auckland and Tauranga have water metering in place for all residences, but in Wellington only around 1% of residential supplies are currently metered.[22]

The same National Performance Review also compares water losses between supply networks. The data for Wellington shows that despite having a higher than average system pressure, the water losses (reported as an infrastructure leakage index), were lower than average, and approaching a threshold where action to reduce losses even further could be uneconomic unless there are shortages.[23]

In their submission to a Wellington City Council Water Committee, Wellington Water warned that "current water consumption and a growing population will lead to water shortages by 2040".[24]

In March 2020, it was reported that Wellington City Council was considering installing water meters for all domestic consumers.[25]

At the time of that report, only 1,200 residential properties in Wellington were using water meters.[26]

In December 2017, the Kapiti Coast District Council reported that there had been a drop in consumption of more than 26% since water meters were installed in July 2014.[27]

Drinking water is subject to a regime of testing under the Health Act to verify that the water meets standards.

The summary results of compliance testing for the 2017/18 year were:[6]

Up until late 2016, bores in the Waterloo well field were considered to be secure. However, a rising trend in bacterial count and E.coli detections triggered a review. At that stage, about half the customers supplied from the Waterloo treatment station received unchlorinated water.

During 2016 and 2017, water supply businesses throughout New Zealand became aware of the severe public health consequences of the Havelock North drinking water contamination incident and the subsequent Government inquiry that recommended all drinking water supplies should be chlorinated.

In 2017, a decision was made by Greater Wellington Regional Council to chlorinate all the water drawn from the Waiwhetu aquifer.[28]

There were two periods during early 2019 when a "boil water" notice was issued to the residents of Martinborough.[29]

An independent report into the first incident found significant shortcomings in the design, operation and management of the Martinborough water supply system. The report revealed that a UV disinfection system failed after a power cut, and untreated water was pumped into the supply pipelines until the following day. A comment was made that it was only a matter of luck that the incident did not lead to a repeat of the widespread illness and deaths that occurred in the Havelock North water contamination in August 2016. [30] Following the contamination incidents, the town water supply was chlorinated, but this introduced a problem with discolouration because the water from some of the water supply bores is naturally high in manganese.[31]

In November 2019, Wellington Water said that Martinborough residents needed to restrict demand to avoid restrictions and also to prevent the water from becoming discoloured if it became necessary to draw water from bores that have a higher naturally occurring manganese content.[32]

In December 2019, the South Wairarapa District Council announced that a manganese extraction plant would be installed that would help keep water clear, and boost supply by enabling use of all four bores adjacent to the Ruamahanga River.[33]

Bulk water supply pipeline across Hutt River at Silverstream Bridge

The supply of water to the Wellington region is potentially vulnerable to significant disruption in the event of failures caused by a major earthquake.

An application in 2017 by Wellington Water for an easement for a storage reservoir referenced a 2009 study conducted by GNS Science of possible earthquake damage to the water network. This study estimated that for a magnitude 7.5 Richter scale earthquake, there would be about 30 breaks on the main trunk pipelines and 60 breaks on the smaller branch lines. There could be as many as 8,000 breaks in the Wellington City local supply network. Bulk water supply and treatment facilities are also expected to suffer damage requiring repair. Wellington Water and Greater Wellington Regional Council estimated that it would take around 60‐70 days to restore bulk water supply to parts of the Wellington metropolitan area.It could take several years to fully repair damage to the local water distribution network resulting from a severe earthquake, as much of the network may have to be rebuilt.[34]

In 2013, GNS Science published a study examining a wide range of issues about the impacts of a large earthquake on Wellington's water supply. Some of the key findings and implications for Civil Defence and Emergency Management from this report include:[35]

• The amount of water people have stored in their homes
• The importance of reservoirs in the provision of water post-earthquake
• People's willingness to collect and carry water from reservoirs to their homes
• The importance of developing alternative sources of water to cater for post-earthquake demand
• The prioritization of water supplies

In 2016, the Wellington Lifelines Group began work on a Regional Resilience Project, with the aim of ensuring that core infrastructure is as resilient as possible and can enable rapid economic recovery following a major earthquake.

In October 2019, the Wellington Lifelines Group published their report "Protecting Wellington's Economy Through Accelerated Infrastructure Investment Programme Business Case".

The appendices to this report include studies of possible impacts of a major earthquake. The base case studies show that in a major earthquake, the Wellington region would be likely to lose its water supplies for a period of between 3 and 6 months, with treated water potentially not available for up to 12 months. A wide range of risk mitigation projects were identified and included in modelling to show the potential improvements in resilience. The risk mitigation projects included works to reduce the risk posed to the bulk water supply that runs parallel to the line of the main Wellington fault. The modelling of outages indicates that the outage time would reduce to between one and three months, if all the identified risk mitigations were implemented.[36]

The report called on its 16 member organisations to help deliver 25 key infrastructure projects across the region over the next two decades, at a cost of $5.3b. It was forecast that implementing these projects would save the country more than $6.1b in lost economic activity in the five years following a major earthquake. The list of 25 proposed projects covers a range of lifeline utilities. The proposed water supply resilience projects are shown below.[37]

In 2017, Wellington Water applied for the designation of an easement required for the construction of a 35 million litre reservoir on land within the Wellington Town Belt, at Prince of Wales Park in the Wellington suburb of Mt Cook. The reservoir provides a significant increase in water storage for the city, and forms part of the city's resilience strategy to help ensure that fresh water is available to residents after a natural disaster or major network failure.In May 2018, an independent panel recommended that Wellington City Council confirm the designation of the easement for the reservoir.[38]

Preparatory earthworks for the project commenced in February 2019.[39]

The 2018/19 National Performance Review published by Water New Zealand compares the average stormwater pipeline age and condition across networks. The data for the Wellington Water network shows that 16% of the pipelines are in poor or very poor condition. The Wellington stormwater network ranks the worst on this measure out of the six large networks nationwide.[19]

The review also includes average pipeline age. The Wellington stormwater network has an average age of 49 years, and ranks as the second oldest of the six large networks.[20]

In June 2020, the Porirua City Council announced that work was underway to increase the resilience and capacity of the local stormwater network. The scope includes the creation of a new wetland. [40]

Wellington's population grew rapidly in the late 19th century after it became the capital city in 1865. There were increasing cases of typhoid and cholera which were attributed to poor sanitation. In 1879 there were 75 deaths in Wellington from typhoid, diphtheria, scarlet fever, measles and cholera – mostly in the central Te Aro area.[41] After some political deliberation, construction of a city wastewater network began in 1893. It cost £175,000 and was completed by 1899.

As part of the early development of the wastewater network, a large pipe was constructed to take wastewater from Manners St through Mt Victoria and out to an ocean outfall at Moa Point on the south coast. This main trunk wastewater line was known as "the interceptor". In the 1930s the interceptor was extended from Manners St through to Pipitea St, as the city's population topped 100,000. As suburbs spread further north to Johnsonville, another extension of the interceptor was made from Ngauranga Gorge and through Ngaio Gorge to connect at Thorndon.[42]

There are four wastewater treatment plants serving the Wellington metropolitan area. Together, they treat about 150 million litres of wastewater on a typical day, using biological and ultraviolet treatment processes. The treated water is discharged to the sea. The sludge resulting from filtration and treatment is de-watered (with this water further treated) and the solid content is sent to landfills.[43][44]

The Moa Point treatment plant handles all the wastewater from most of Wellington city, other than Karori and some northern suburbs. Treated wastewater is discharged via a 1.8 km ocean outfall into Cook Strait. Sludge is separated from the wastewater at the plant, and pumped to a landfill site at Carey's Gully, where it is dewatered and placed into a landfill.

The Seaview plant handles wastewater from Upper Hutt and Lower Hutt. There is an ocean outfall at Pencarrow Head.

A treatment plant located at Rukutane Point to the south-west of Titahi Bay beach handles wastewater from the northern suburbs of Wellington and Porirua city. There is an ocean outfall from the plant.[45]

A separate wastewater and treatment system serves the Karori area. Treated wastewater is piped out to the South Coast.

The 2018/19 National Performance Review published by Water New Zealand compares the average wastewater pipeline age and condition across networks. The data for the Wellington Water network shows that 33% of the pipelines are in poor or very poor condition. The Wellington wastewater network ranks the worst on this measure out of the six large networks nationwide. (The next worst is Christchurch, with only 12% in poor or very poor condition).[19] The review also includes average pipeline age. The Wellington wastewater network has an average age of 53 years, and ranks as the second oldest of the six large networks.[20]

In March 2020, Wellington Water reported the discovery of severe corrosion in the large main trunk sewer (the interceptor) over a length of 250 m in a section close to the treatment plant near Moa Point.[42]Work commenced on re-lining the affected section of the interceptor in April.[46]

As part of a submission to a Porirua City Council committee in 2018 in relation to renewing resource consents, Wellington Water provided a background document about the issues in the Porirua wastewater system. The issues reported included:[47]

• poor existing freshwater quality in the Porirua catchment
• frequent overflows from wastewater networks into freshwater and coastal water during periods of wet weather, and overflows from the wastewater treatment plant into coastal water
• inflow and infiltration from stormwater into the wastewater network
• ageing network prone to failures and with insufficient capacity to accommodate future growth
• insufficient capacity of the treatment plant to accommodate future growth

In February 2020, the Mayor of Porirua announced the establishment of a roving team to search for issues such as cross connections in stormwater and sewage pipes. As part of that announcement, it was revealed that more than half of Porirua's wastewater pipes are in a poor condition, and that it will cost close to $2 billion over the next two to three decades to bring them up to scratch.[48]

Ōwhiro Bay is located on the Wellington south coast. The shoreline is within the Taputeranga Marine Reserve. There have been persistent problems with sewage pollution of the Ōwhiro Stream and beach for at least ten years, and the beach has been closed for swimming for long periods.[49][50][51]

In March 2020, Wellington Water announced that it had found and resolved incorrect connections of wastewater into stormwater systems at five locations in a suburb in the stormwater catchment area of the Ōwhiro Stream. Wellington Water said that the mistake occurred when the subdivision was built about eight years ago, and there were likely to be more cross-connections that it had yet to identify.[52]

In October 2018, a series of errors and omissions in the management of the Porirua wastewater treatment plant led to a spill of approximately 5000 cubic metres of wastewater and solids from the outfall into a small bay adjacent to Titahi Bay beach. In a subsequent hearing in the Environment Court in September 2019, Wellington Water was fined $65,000 for the illegal discharge.[53]

Warning signs were posted at Titahi Bay beach in late February 2020, warning against swimming because water quality monitoring had revealed high levels of faecal coliforms. The water at the beach was deemed unsafe for recreational use, including for swimming, fishing or collecting seafood.[54] A further beach closure notice was posted in mid-March 2020.

Wellington Water stated that likely causes such as cross-connections from wastewater to stormwater pipes or damaged pipes provide intermittent flows, so contamination is not constant. As a consequence, some issues can lie undetected for years, while tracking faults can take weeks and sometimes has to be delayed as more urgent repairs take priority. In a statement acknowledging public concern, Wellington Water stated that the recent water quality warning for Titahi Bay beach was not linked in any way to the nearby wastewater treatment plant, and that resolving localised contamination events such as this is the aim of the proposed roving water quality team that Porirua City Council is looking to introduce in the new financial year.[55]

The beach was still considered unsafe for swimming on 30 April 2020. However, Wellington Water reported that they had located a plumbing fault in the catchment feeding into Titahi Bay beach and were working to get this fixed. [56]

On 20 December 2019, a wastewater pipe built in the 1930s collapsed beneath the intersection of Willis and Dixon Streets in the central business district, leading to the diversion of untreated wastewater into Wellington harbour at an initial rate of up to 100 litres a second. The broken pipe serves much of the central city, taking wastewater to the interceptor (or main trunk sewer), that leads to the Moa Point wastewater treatment plant. The public were warned not to swim in the inner harbour, but local iwi placed a rāhui on the entire Wellington harbour.[57]

An emergency above-ground pipe was placed along Upper Willis street—closing it to all traffic—to bypass the failed underground pipe while permanent repairs were made. The swimming restriction on the whole of Wellington Harbour was lifted on 26 December. However, the area of the inner harbour from the Whairepo Lagoon entrance past the dive platform to the Clyde Quay wharf remained off-limits because of a “separate network issue”.[58]

Willis Street was eventually re-opened at the end of March 2020, after the permanent replacement had been installed beneath the road, and the temporary above-ground pipe removed.[59]

In January 2020, there was a failure of pipelines carrying sludge pumped at high pressure from the Moa Point treatment plant to the landfill at Carey’s Gully. The pipelines are 9 km long and are about 25 years old. There are two in parallel allowing one to operate while maintenance can occur on the other pipe. In this incident both pipes failed at the same time.

To avoid discharging the sludge into the ocean, a fleet of sewage trucks was mobilized to carry about one million litres of sludge a day to the dewatering plant at Carey’s Gully. Up to 150 round trips each day were required, with trucks sometimes operating around the clock to keep up with the volume.

The break in the pipelines was located 200 m inside a sewage tunnel beneath Mt Albert, making repairs a significant challenge. The repair solution required the manufacture in Germany of a custom-made polyester woven liner. This liner was winched from one end of each pipe to the other, and then expanded to essentially act as a new pipeline within the old one. Specialists from the manufacturer flew to New Zealand to assist in the installation, but were required to spend 14 days in isolation because of the border restrictions imposed in response to the COVID-19 pandemic.[60][61][62]

In April, the Wellington City Council agreed to borrow $16 million to fund repairs to the sludge pipelines, together with the on-going costs of transporting sludge via truck from the Moa Point treatment facility to the landfill site while the repairs were carried out.[63] On 24 May, Wellington Water announced that the first of the two sludge pipelines had been repaired and put into service, allowing the sludge trucking operations to end.[64]

Almost half a million litres of partially and fully treated wastewater was discharged into the Ruamahanga River near Martinborough in two incidents in January 2020, as a result of issues at a treatment plant. Under suitable conditions, discharging fully treated wastewater to the river is a consented activity. However, when the river level is low, as in this case, this type of discharge is a breach of the resource consent.[65][66]