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The Council is upgrading the reservoirs at Castle Hill with the installation of two new 500m3 litre reservoir tanks over the course of 2022.

The Castle Hill water supply currently has three 500m3 timber reservoir tanks. These wooden tanks were built in the early 1980s and are due for renewal in the next 10 years. As part of the upgrade of the Castle Hill water supply, the Council has brought forward the upgrade of two of these tanks.

During 2022 the Council will be installing two modern 500mglass fused to steel tanks.

These tanks have been designed to an importance level 4 (IL4) rating - which means these reservoirs should remain operational following a disastrous event. The design parameters for IL4 include building to withstand earthquake, wind and snow events among others.

This will provide for new, long-term and higher safety rating water storage tanks for the township as it grows.

During the construction of these tanks, the reservoir capacity will be reduced as one tank at a time will be offline for the duration of works. This means during high use times, or in case of shutdowns to the water source (such as a heavy rain event) a conserve water notice may be required.

Subscribe to receive water alerts including conserve water notice.

To reduce the chances of conserve water notices being required please be mindful of your water use and use water wisely through things like reducing car washing and smart watering. Find tips to save water .

You can also find a live update of the reservoir levels below.

Timeline and Progress updates

27 January 2022

A full supply wide water shutdown will be required for up to six hours to prepare for the construction of the first tank. A shutdown notice will be sent out to all households before this takes place with more information. Please be aware that there will be no water supply for this time.

31 January - mid May 2022 (weather permitting)

Construction of the first tank.

May – June 2022

Final connection of the reservoirs to the water network, commissioning of the new Water Treatment Facility and switch over of village water supply from the existing treatment system to the new treatment system.

October - December 2022

Construction of the second tank.


Frequently Asked Questions

What will the new tanks look like?

The new tanks will be taller than the existing tanks due to IL4 design requirements and will be constructed in a low reflection dark-green coloured glass fused to steel panels.

What is the design life of the new reservoirs?

These structures have been designed to a 50 year design life.

Where can I find further information about the Importance levels (IL)?

Schedule 1 (The Building Code) of Building Regulations 1992 provide further information on the various importance levels here: Building Regulations 1992 (SR 1992/150) (as at 15 November 2021) Schedule 1 The building code – New Zealand Legislation

What events are IL4 structures designed for? 

IL4 structures designed in line with AS/NZS1170 with a 50 year design life (the design specifications for the Castle Hill reservoir tanks) are designed to have an annual probability to withstand a
1/2500 wind event
1/500 snow event
1/2500 earthquake event.

How does the Council stop dirty water from getting into the drinking water network during flood events?

Turbidity (dirt in the water) is measured on the raw water pipe (untreated water straight off the river) close to where it enters the water treatment site. When water turbidity rises - for example during a flood event - a control valve closes, stopping the dirty water from being able to enter the existing treatment and reservoirs. Instead, this high turbidity water is flushed out of the system.

What improvements will the new treatment system offer?

The existing water treatment system only offers turbidity control and water chlorination. This means this system is not currently compliant with the Drinking Water Standards for New Zealand 2005 (revised 2018) (DWSNZ) and needed to be upgraded to reach compliance.

The DWSNZ and Selwyn District Council’s Castle Hill Water Safety Plan require a multi-barrier approach to water treatment to ensure public health. The new treatment system includes three key barriers for public safety. These are filtration, UV disinfection and an upgraded chlorination system. Turbidity control will also be maintained. The new treatment facility allows us to automate the treatment process and gives a greater ability to test and monitor the water and control processes throughout the treatment process.

What do I do if I see a water leak?

If you see a water leak you can let us know immediately through the Snap Send Solve App, which you can download to your phone.  Or you can:

  • give us a call on 0800 SELWYN (735 996)
  • send us a message through our contact us page ,
  • email our Customer Services team
  • visit us at one of our customer service centres in the libraries at Darfield, Leeston, Lincoln or Rolleston, or our Rolleston offices.