Learnings from the November 2022 Morrinsville Water Event
Severe weather in Morrinsville recently caused havoc with the water treatment plant, resulting in critical water restrictions for the Morrinsville community for several days. Here we share what happened at the plant, what we learnt and what we are doing to prevent this occurring again.
Severe weather on Wednesday 23 and Thursday 24 November in the Morrinsville water catchment stirred up lots of dirt and debris in the raw water supply. This isn't uncommon after major weather events - it just slows down the water treatment process, taking longer to process safe drinking water that meets the Taumata Arowai Drinking Water Quality and Assurance Rules. That is why we also have stored treated water to draw on during these periods.
By Saturday 26, the treatment process appeared to be coming right, with treatment capacity at the plant increasing. However, the team noticed problems with the water pH levels in the treatment process, and began working to correct this. The pH meant the plant wasn't operating at top capacity and they continued to try to manually balance the pH - this is a long process. As it takes a couple of hours of treatment before we can see the results of the dosing. As time went on, we didn't appear to be making any progress refilling the reservoir, so we introduced water restrictions, asking the community to reduce water use while we continued to troubleshoot at the plant.
At midnight on the 26th Mt Misery storage reservoir was below 50% capacity, 8am on the 27th the level was reading 40% and by 4pm the level was 20.3%. It was obviously unusual to have a consistent level in the reservoir for so long, so one of our team members headed out to the site to manually measure the reservoir level. At this point we discovered the sensor was faulty and the supply of stored drinking water was down to 4%.
Council established an emergency response team, and notified the community to urgently conserve water and arranged water tanks to be available at locations around town. This information was shared widely on digital channels. We also tried to make contact with representatives from the Ministry of Education (who were uncontactable) for the schools to be informed and the Chamber of Commerce. We also arranged for water tankers to continue to be available for the community.
The team continued to troubleshoot at the water treatment plant, including external experts from Auckland. These Process Control Engineers who are available to provide technical support can normally access our systems remotely, but problems at the plant were significant enough that they had to attend in person.
Late on Monday 28 November, testing found low Free Available Chlorine (FAC) levels at 2 (of 4) network testing sites in Morrinsville. As a precaution, a boil water notice was introduced, there were more reasons than just low FAC for putting a boil water notice in place. The Fonterra bore which came on as an additional water source to ensure that network remained pressurised, has untreated water, and the reduced pressure in the network, which can allow dirty water to flow back in, also played a part. These factors pose risks to public health. The national Emergency Mobile Alert system was used to ensure people were aware of this. Water tankers continued to be available around town, and council arranged to supply bottled water to schools and rest homes.
Over the course of several days we continued to sample water from all over town to check for any contamination. No contamination was detected at any stage. The Boil water notice was continued as a precaution.
On Tuesday morning (29 November), parts of town woke to find they were without water. By this stage the water treatment plant was stabilised and was increasing treatment volume - but it takes time to refill the network. It has to be done slowly to avoid trapping air in the pipes and creating an "air hammer" effect which can lead to pipe breakage and further disruption.
Water supply was restored to all areas by midday on Tuesday 29 November. Water restrictions eased slightly from 3pm that afternoon, allowing short showers. These were eased further on Wednesday 30 November, shifting back to Level 4 restrictions (all outdoor watering banned and reducing household use where possible).
The precautionary boil water notice remained in place until Friday 2 December. Water restrictions remained in place for a few days longer while the reservoirs were refilled, and were lifted on Monday 5 December.
