New Reservoir for Karori

22 February 2010

Water is a precious resource, essential to many facets of our lives. The Council must supply some 350* litres of water a day for each person in the city. It's something like 60 million litres a day - and we constantly monitor our water supply network to make sure it's up to the job.

Karori School students sampling the drinking water

Karori School students sampling the drinking water

The network is huge - it includes 81 reservoirs and tanks, just over 1,000 kilometres of pipes, 33 pumping stations and more than 100,000 fittings, valves and controls.

We have an ongoing programme aimed at strengthening the network. Many millions of dollars are being spent on bigger reservoirs that can hold more water and withstand earthquakes.

Our engineers' focus is now on Karori - and the replacement of two reservoirs in Messines Road. The tanks are critical to the security and continuity of water supply to 'New Zealand's largest suburb' because they feed six other reservoirs around Karori.

The tanks, built in 1925 and 1935, have a combined capacity of 3,500,000 litres. We will replace them with a new single reservoir - on the same site - which will contain 6 million litres of water and allow for population growth over the next 75 years. The reinforced-concrete tank will also be fitted with an automatic shutoff valve. This will ensure the reservoir will not be drained if the local pipe network is damaged in a major earthquake. We've set aside $7.35 million to pay for this work.

The design will use some of the existing reservoirs' walls and floors, which will avoid deep excavations adjacent to other properties, and minimise the amount of demolition work, as well as the noise and material we will have to remove while the first stage is constructed.

We've decided to take a two-stage approach to development. First, we'll decommission the oldest (1925) reservoir. This will limit the water supply, so we're going to do this in winter when demand is lowest.

When finished, the new reservoir will be buried and covered with landscaped topsoil and grass. We believe its appearance and road frontage will be an improvement on the current site.

Resource consent has been granted for the new reservoir, and design and tender documentation has been completed. The entire project, which will start later this year, will take around two years to complete.

* This figure is based on total water supplied, less the metered commercial use, divided by resident population. Because this figure can be affected by changes in resident and Council activities, it is used when measuring water usage trends as part of managing water demand.