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Importance of conserving water
Christchurch has a clean and high-quality water supply, primarily drawn from aquifers deep underground. For many years, the water was simply pumped from wells all over the city, straight into the water pipes for the households to use, however this is no longer sustainable in the long term. Compared to other cities in New Zealand, Christchurch has higher than average water usage and this is a growing issue as the city gets bigger and our infrastructure needs upgrading.
From July 2022, Christchurch ratepayers will be charged for excess water use. The Christchurch City Council has stated that this is to help reduce the extreme demand on the water supply network, particularly the peak demand over summer. Up until now, the provision of water supply to the city has been funded primarily as a targeted rate to all serviced properties, without taking residential water usage into account. The Council hopes that by beginning to charge households for excess water usage, there will be a reduction in water use of around 20 to 30 percent, similar to what has been seen elsewhere in the country when charges have been introduced.
To make use of our water resources more efficiently and sustainably, we need to aim to only take the water we need, at the taps, at the meters, and at the pumps. The new Excess Water Use targeted rate will contribute to that goal, but so will the data which has been generated in the process of executing the new rate.
Value of open data
The Christchurch City Council has made a Water Reporter tool publicly available, so that households can understand what their water usage is, and take steps to reduce it before the new rate comes into effect. Making residential water usage data open and transparent like this is an important step in lowering usage, and towards making the entire water supply network operate more efficiently. Opening up data also allows others to benefit and add value to it in ways that the data owner may not have considered or be incentivised to pursue.
FME to automate dataset generation
Feature Manipulation Engine (FME) is a data integration platform, which enables the transformation and migration of data between hundreds of systems and formats. With it, we can automate the generation of a water usage dataset from the Water Reporter tool provided by the Christchurch City Council. A process like this can be set up in less than a day and enable a range of analysis to be undertaken.
Visualising water use
With the data collected, we looked at the patterns of water usage across Christchurch. Mapping each property’s water usage clearly shows that the average daily usage is not distributed evenly over the city. As reported by the Christchurch City Council, the average Christchurch household uses 540 litres per day, which is less than the new excess limit of 700 litres at which point people will be charged. However, this mapping exercise also showed average usage near 1000 litres per day per household across Prestons and Parklands. In comparison, Sydenham and Spreydon use half as much water on average, at under 500 litres per day per household.
Visualising water consumption spatially like this can inspire inferences as to the causes of high consumption. Water usage is higher in areas with sandy soils. Areas with higher density residential living have lower water usage per household. There are some streets where every household has high water usage, which could be due to neighbourhood effects, and may require an approach beyond simply charging for excess water to collectively reduce their usage.
It can also be easy to think that reducing water usage is somebody else’s problem, yet almost every street in the city has at least one high water user. One colleague checked the Water Reporter, and it was only by luck discovered they had a large water leak when it reported that they had been using 4500 litres per day. Nearly 1% of properties have water usage over 3000 litres per day, numbers which are hard to achieve without a leak. For many, the rates bill arriving this year could be the first notice they receive about their leak. How much are you using?
Summary
The publishing of water usage data for Christchurch households does a great service to raise awareness about high water usage for the citizens of Christchurch. It also represents an opportunity for the data to be used for further good, to validate published statistics around water usage, to manage the incidence of leaks across the city. Over time, it will allow us to directly observe the effect of the new excess water rate on our city’s water usage. The release of open data should always be encouraged, especially when it presents such a clear benefit to everyone.
