Monitoring fluoride levels at water treatment plants

We have sensors for monitoring the level of fluoride in the water at each of the four metropolitan Wellington drinking water treatment plants. These readings are taken automatically. The daily averages per plant are calculated (using an arithmetic mean method) and provided monthly to Ministry of Health.

Our aim is to maintain a steady level of fluoride in the water at treatment plants that meets the Ministry of Health fluoride target of 0.7 – 1.0ppm. This is the amount recommended by the Ministry of Health and the World Health Organisation to provide protection against tooth decay.

We also have controls in place to ensure we never supply consumers drinking water over the Maximum Acceptable Value (MAV) of 1.5ppm.

The latest data (February 2025) on the levels of fluoride in the water supplied to Wellington:

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Mārua	Upper Hutt, North and West Wellington	99.5%	0.83
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	92.3%	0.76	Testing the fluoride dosing system with the Automation team. Testing plant pumps and running checks.
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	98.7%	0.81
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	98.9%	0.8

Listed below are the percentages and monthly average fluoride levels that the plants achieved for the previous months

January 2025

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Mārua	Upper Hutt, North and West Wellington	99.3%	0.87
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	71.3%	0.65	Dosing was turned off on 23/1/2025 due to a spike in fluoride and some issues with the analysers. Following direction from management dosing was switched to offline until investigations could be completed.
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	96.5%	0.81
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	98.9%	0.8

December 2024

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)
Te Mārua	Upper Hutt, North and West Wellington	98.4%	0.79
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	97%	0.84
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	97.2%	0.82
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	96.6%	0.83

October 2024

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)
Te Mārua	Upper Hutt, North and West Wellington	99.9%	0.84
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	97.6%	0.84
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	97.7%	0.83
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	95.8%	0.84

November 2024

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)
Te Mārua	Upper Hutt, North and West Wellington	99.3%	0.86
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	95.5%	0.83
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	96.4%	0.8
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	97.5%	0.84

September 2024

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Mārua	Upper Hutt, North and West Wellington	98.9%	0.84
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	89.9%	0.79	Powder in hoppers has got moisture in it after rain water got into the storage room. Operations are working as quickly as possible to get dosing back online.
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	97.1%	0.83
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	98.7%	0.84

August 2024

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Mārua	Upper Hutt, North and West Wellington	99.3%	0.82
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	92.5%	0.8	Dosing off due to unplanned shutdowns.
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	92%	0.79	Dosing system faults.
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	95.7%	0.86

July 2024

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)
Te Mārua	Upper Hutt, North and West Wellington	98%	0.83
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	97.8%	0.83
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	88.7%	0.81
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	99.8%	0.88

June 2024

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Mārua	Upper Hutt, North and West Wellington	98.9%	0.84
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	97.1%	0.84
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	88.7%	0.77	Pumps being replaced, project work and multiple issues with dosing caused percentage to drop out of compliance range.
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	98.5%	0.86

May 2024

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Mārua	Upper Hutt, North and West Wellington	93.5%	0.8	Planned maintenance and project work affected percentage.
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	97.7%	0.83
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	96.5%	0.8
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	98.3%	0.86

April 2024

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)
Te Mārua	Upper Hutt, North and West Wellington	96.6%	0.83
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	97.7%	0.83
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	96.5%	0.8
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	98.5%	0.86

March 2024

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Mārua	Upper Hutt, North and West Wellington	84%	0.73	Planned maintenance and unplanned shutdowns due to faults with dosing pumps.
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	94%	0.8	Planned maintenance and trials for diesel pumps.
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	97.2%	0.83
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	99%	0.87

February 2024

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Mārua	Upper Hutt, North and West Wellington	98%	0.81
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	52%	0.5	Running of Diesel pumps, batching faults and lower dosing for implementation of new product.
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	86%	0.72	Dosing off for maintenance of dosing system.
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	92%	0.8	Some issues with the fluoride hopper and communications to the fluoride building,

January 2024

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Mārua	Upper Hutt, North and West Wellington	96%	0.8
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	94%	0.77	Dosing turned off due to issues with batching tank and subsequent maintenance to mitigate issues.
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	90%	0.8	Planned works, maintenance, and some system faults.
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	97%	0.85

2023

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Marua	Upper Hutt, North and West Wellington	100%	0.77
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	100%	0.77
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	94%	0.79	Fluoride levels at the Gear Island Water Treatment Plant were under the 95% mark this month we are trialling and testing new fluoride analysers. Fluoride analysers read the fluoride levels in the drinking water.
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	91%	0.76	Fluoride levels at the Wainuiomata Water Treatment Plant were under the 95% mark this month as we had to turn off the water treatment plant due to wet weather events in January.

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Marua	Upper Hutt, North and West Wellington	97%	0.77
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	100%	0.78
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	93%	0.76	Fluoride levels at the Gear Island Water Treatment Plant were under the 95% mark this month as we are trialling and testing the new fluoride analysers (which read the fluoride levels in the drinking water) and replacing a pump in the fluoride facility. This required us to turn off the facility from time to time throughout the month.
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	75%	0.70	Fluoride levels at the Wainuiomata Water Treatment Plant were under the 95% mark this month as we had to turn off the water treatment plant due to wet weather events in February.

Water Treatment Plant	Areas Supplied	Percentage met (portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Marua	Upper Hutt, North and West Wellington	100%	0.81
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	97%	0.76
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	88%	0.80	Fluoride levels at the Gear Island Water Treatment Plant were under the 95% mark this month as we were trialling and testing new fluoride analysers (which read the fluoride levels in the drinking water).
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	81%	0.71	Fluoride levels at the Wainuiomata Water Treatment Plant were under the 95% mark this month due to planned maintenance work, which meant we had to turn off the facility while this work was underway.

Water Treatment Plant	Areas Supplied	Percentage met (portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Marua	Upper Hutt, North and West Wellington	97%	0.77
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	94%	0.74	Fluoride levels at the Waterloo Water Treatment Plant were under the 95% mark this month due to some updates undertaken to the algorithm in the controls system at the plant.
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	80%	0.77	Fluoride levels at the Gear Island Water Treatment Plant were under the 95% mark this month we experienced some issues with the fluoride instruments in the first half of the month.
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	84%	0.71	Fluoride levels at the Wainuiomata Water Treatment Plant were under the 95% mark this month as we had some issues with the fluoride instruments and we had to commission a fluoride dosing pump.

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Marua	Upper Hutt, North and West Wellington	100%	0.8
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	100%	0.79
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	90%	0.77	Fluoride Dosing off for planned work
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	90%	0.76	Fluoride dosing off for planned replacement of instruments

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Marua	Upper Hutt, North and West Wellington	94%	0.79	PLC maintenance
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	100%	0.79
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	94%	0.79
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	94%	0.8	Plant off on some days and some testing of high residual alarms

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Marua	Upper Hutt, North and West Wellington	95.6%	0.83
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	96.5%	0.79
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	91.7%	0.76	Fluoride levels at the Gear Island Water Treatment Plant were under the 95% mark this month due to some operational issues with the fluoride facility.
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	97.5%	0.81

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Mārua	Upper Hutt, North and West Wellington	99%	0.81
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	97%	0.79
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	80%	0.7	Plant shutdowns due to UV reactor, pump, dosing issues and planned works.
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	97%	0.81

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Marua	Upper Hutt, North and West Wellington	99%	0.85
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	98%	0.81
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	83%	0.74	Multiple pump maintenance events and planned shutdowns.
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	96%	0.83

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Mārua	Upper Hutt, North and West Wellington	68%	0.62	Fluoride dosing turned off for an extended period due to leaks in the transfer pumps. Repairs required.
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	49%	0.46	Health and safety risk identified, some equipment being switched out.
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	88%	0.75	Scheduled work on the pumps throughout the month.
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	90%	0.78	Health and safety risks identified, dosing was turned off until resolved.

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Mārua	Upper Hutt, North and West Wellington	99%	0.85
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	84.1%	0.71	Fluoride facility was turned off for bi-annual reservoir clean and some minor analyser issues.
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	52.4%	0.69	Server upgrades by contractors and issues with pumps.
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	98%	0.87

Water Treatment Plant	Areas Supplied	Percentage met (Portion of readings within Fluoride target)	Average Dose (ppm)	Comments
Te Mārua	Upper Hutt, North and West Wellington	99.2%	0.84	Fluoride dosing turned off for an extended period due to leaks in the transfer pumps. Repairs required.
Waterloo	Hutt City, CBD, Eastern-Southern Wellington (excl. Petone, Stokes Valley)	93.2%	0.78	Health and safety risk identified, some equipment being switched out.
Gear Island (taken at the supply main)	CBD, Eastern-Southern Wellington Only	50%	0.7	Scheduled work on the pumps throughout the month.
Wainuiomata	Wainuiomata township, Eastern-Southern Wellington	99.2%	0.87	Health and safety risks identified, dosing was turned off until resolved.

Other Drinking Water Analysis

We complete additional chemical analysis of the water supply, as part of the requirements set by the Drinking Water Standards.

This analysis is performed by Eurofins, which is an independent IANZ-accredited laboratory.

You van view the annual chemical analysis here.

Data Usage Disclaimer

We aim to ensure the data published on this page is accurate and up-to-date. Wellington Water does not accept any responsibility for the use of or reliance on the data and shall not be liable to any person on any ground for any loss, damage or expense arising from such use or reliance.