Wellington Region water supply
On average we supply over 160 million litres (ML) of water per day to Upper Hutt, Lower Hutt, Porirua and Wellington, and around 4 million litres of water per day to Greytown, Featherston, Martinborough and Pirinoa.
Learn more about where your water comes from in Wellington or in South Wairarapa on the pages below.
Catchments and storage lakes
Water supplied to the Wellington metropolitan area comes from three sources:
- Hutt River/Te Awakairangi
- Combined flow of the Wainuiomata and Orongorongo rivers
- Waiwhetu Aquifer - a natural underground reservoir beneath the Hutt Valley that is fed by river water seeping down into the ground
The river sources are supplied from special catchment areas that are protected to keep pollution to a minimum. They are upstream of housing, away from people and are controlled for pests.
We only take and use the water we need from the rivers. We ensure enough water remains flowing downstream so that the natural habitat can thrive and the rivers can continue to be used for recreational activities. There are times when there isn’t enough for us to take to meet public demand, so when the water in the rivers gets low, typically during the summer months, we have to supplement the supply with water stored in two large storage lakes (Macaskill Lakes at Te Marua).
Hutt Water Collection Area
The Hutt Water Collection Area covers almost 9,000 hectares of bush-clad mountains and valleys at the southern edge of the Remutaka Ranges. The collection area is about equal in size to a square with the length of each side the same as the distance between Wellington's railway station and Petone. Rainwater collects in tributary streams that flow into Hutt River. We have a weir (low dam) at Kaitoke, north of Upper Hutt, where water is taken from the river, strained to remove sticks, stones, leaves and silt, and is then piped through tunnels to the Te Marua Water Treatment Plant. We are allowed to take up to 150 million litres of water per day from the Hutt River, provided an adequate flow is maintained downstream of the weir. The Hutt Water Collection Area provides about 40 percent of the water we supply each year, on average.
Macaskill Lakes at Te Marua
We have two large storage lakes at Te Marua - the Macaskill Lakes - as back-up to the Hutt River supply. The lakes are filled from the river when it is clean and there is plenty of water available. Stored water is pumped back to the treatment plant when there is not enough water in the river to meet public 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 around 17 metres deep and have a combined useable capacity of approximately 3,350 million litres. In a severe drought the Macaskill Lakes can supplement supply for 2-3 months or longer if needed, depending on the level of demand and the amount of water available from other sources.
Wainuiomata/Orongorongo Water Collection Area
The Wainuiomata/Orongorongo Water Collection Area is part of the Remutaka Ranges to the east of Wainuiomata. The collection area covers 7,600 hectares. Five low dams (weirs) with intakes and pipes provide water to the Wainuiomata Water Treatment Plant. Intakes on the Wainuiomata River and George Creek provide around 15 percent of our annual water supply, on average. In the Orongorongo Valley, weirs on the Orongorongo River, Big Huia Creek and Little Huia Creek provide around five percent of annual water supply, on average. A 3.2 kilometre long access and pipeline tunnel links the Orongorongo Valley intakes to the Wainuiomata Valley and the treatment plant.
We must leave a minimum water flow equivalent to 8.6 million litres per day in the Wainuiomata and Orongorongo Rivers, downstream of our weirs. Unlike Te Marua, there is no untreated water storage at Wainuiomata. If river levels are very low or the rivers are in flood the treatment plant is turned off temporarily.
Waiwhetu artesian aquifer
The Waiwhetu artesian aquifer is a zone of water-holding 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 our wells and is naturally filtered while underground. We monitor the aquifer closely to ensure we leave enough water in it to maintain pressure, so that sea swater cannot enter via the harbour springs. The Waiwhetu aquifer provides around 40% of the annual water supply on average, but this can increase to nearly 70% on a daily basis in summer when river supplies dry up. This makes the aquifer critical for our drought resilience.
South Wairarapa water supply
We supply 4.1 million litres of water per day (on average) to Greytown, Featherston, Martinborough and Pirinoa.
Drinking water in South Wairarapa comes from four sources:
- Four bores that take water from next to the Waiohine River, supplying both Featherston and Greytown
- A single groundwater bore in Memorial Park, Greytown, supplying Greytown only. The bore is recharged from the Waiohine river
- Three bores that take water from next to the Ruamahanga River, supplying Martinborough
- One groundwater bore supplying Pirinoa
Featherston and Greytown water collection area
The towns of Featherston and Greytown get their water from the Waiohine River. The catchment of the Waiohine River is in the Tararua Ranges and is covered in native bush. The bores are adjacent to the river on Waiohine Valley Road, north of Woodside. Water from the Waiohine River is pumped to the treatment plant and is disinfected using UV treatment and Chlorine.
The treated water is stored in storage tanks before the water is piped along Underhill Road to Featherston and along Woodside Road to Greytown. There are also storage tanks in Featherston in Boar Bush Gully Road.
Water from the bore at Memorial Park is also treated using UV and chlorine, and is supplied directly into the water supply network.
Martinborough water collection area
Martinborough’s water supply is taken from groundwater that is pumped from four bores at Herricks Wells. These bores are on farm land close to the Ruamahanga River. From Herricks Wells water is pumped to a treatment plant where it is disinfected using UV and chlorine, and onto the town’s water network. At the far end of the network there are four reservoirs which store excess water, which flows by gravity into the pipe network.
Pirinoa water collection area
The water supplied to Pirinoa is taken from one bore, and is treated using ozone, filtration, UV and chlorine and is then stored in two storage tanks. The treated water is then pumped into the town pipe network.
Pipe and tapware effects
All drinking water can dissolve very small amounts of metals, this is called “plumbosolvency”. Our treatment processes adjust the pH to reduce the water’s aggressiveness on pipework and tapware. However, there is the potential that water sitting in a plumbing fitting, if unused for several hours, may accumulate minute traces of metals which can contain lead, nickel, cadmium, copper and antimony.
Although the health risk is negligible, we recommend that you flush a mugful of water from your drinking-water tap each morning before use. This should remove any water that was left in your fittings, and metals that may have dissolved from the plumbing fittings. All households are advised to take this precaution, whether they are on public or private water supply.
How do I tell if my fittings will accumulate small traces of metals?
In New Zealand it’s typically the older plumbing/fittings which come in to contact with water that are the source of heavy metals.
If you want to know more about your fittings check with your plumber, or you can contact Wellington Water on 04 912 4400. See Blue staining