18 February 2018
The aquifer level at the water supply bores continues to drop. We have reduced the output from the pumps twice now and will have to do so again today to protect the pumps from being damaged. The reduction to date has reduced the flow into the reservoirs from 60 l/s down to 46 l/s. This is a reduction of 24%. Today’s change will take that to 30%.
Residents have made significant water savings in the last 10 days. There has been a reduction in peak demand of 25%. This is allowing the reduced volume of water available from the pumps to continue to meet demand and provide sufficient quantities of water for firefighting. As the aquifer continues to fall and there are further cutbacks at the pumps this will need to continue and for there to be some additional savings, particularly on hot evenings.
The weather forecast has some rain predicted for the end of the week. This will alleviate the situation a little for a short while but more will be needed to bring the aquifer back to a good operational level.
11 February 2019
Thank you and congratulations to the Renwick Community. After we had to reduce the output from the wells, Renwick has stepped up and reduced its water demand over the peak period of 5:00 pm to 9:00 pm. This has enabled the reservoir to continue to operate at good levels. Please note however, if we don’t get some rain in the next ten days and river levels increase, we are likely to have to make further cut backs at the wells.
Thank you also to members of the Water User Group and Smart & Connected for their assistance to deliver flyers to all letterboxes.
7 February 2019
Aquifer levels at the Renwick water supply bores has dropped to 1.0 metre above the pumps. At this level the rate of water extraction will have to be reduced to protect the pump from damage if air is "sucked" into it. When this occurs the volume of water available to fill the reservoir is reduced by 15 to 20%. The water used by the community has to be reduced by a corresponding volume to avoid Renwick running out of water during peak demand. Council is asking Renwick residents to achieve this voluntarily. A 20% reduction will be achieved if the peak demand between 5.00 pm and 9.00 pm is kept below 45 litres per second; at present the peak demand in this period has been 60 litres per second.
Council has commenced sending out an Antenno alert and placing a note on the web site when demand is exceeding the limit of the bore pumps. This will assist residents to reduce water demand when it counts.
If reductions are not achieved water restrictions will have to be imposed early next week.
31 January 2019
Today’s graphs have some green circles pasted on them. This is showing periods of high demand when the volume of water being used is greater than the volume of water produced by the bore pumps at the wells. When this occurs the volume of water is depleted in the reservoir. This can be sustained for short periods but if the reservoir gets too low there is only a small amount of water then available for firefighting. Note how low the reservoir dropped to on Sunday night. The level on this occasion got down to 30% remaining.
We have commenced placing a note on Council’s web site when water availability from the bores is being exceeded by demand, this is also sent out on Antenno. This provides real time feedback to the community on the impacts of high water demand (irrigation). The message reads:
Renwick Water Demand
Water demand has reached 55 litres per second. Residents are urged to reduce water use especially irrigation use for the next two hours. This will ensure the network continues to supply water at good pressure and to meet the requirements for firefighting.
The need to limit irrigation is going to become particularly important in the next few weeks. The aquifer level is dropping quite quickly now that Wairau River flows are very low. The aquifer at the Renwick supply bores is dropping about 100 mm per day. At this rate within 10 days we will have to reduce the volume of water being taken from the wells. When this occurs water demand will not be able to exceed 50 litres per second during the peak periods. If it does the reservoirs will probably run dry leaving Renwick with no water.
Residents are urged to voluntarily limit their use of water for irrigation to avoid this and the necessity for imposed water restrictions.
Water supply updates via the Antenno App
We now have a new way of keeping you in touch with water supply updates. We’ll be using an app called Antenno, which is free to download.
Renwick water supply updates
The Renwick water demand graphs have been put up on the website for the first time this summer. Renwick residents have carried on from last year, making water savings voluntarily. This has been a great effort.
The graphs are being put up now as a tool to help residents continue with water savings and to show the impacts of their efforts.
In the early part of the summer the water level in the aquifer at the supply wells has been very healthy. However levels are now starting to drop as river flows decrease. If the water level drops below 1000 mm at the wells the volume of water able to be taken will have to be reduced.
Water demand is being met throughout the system but with the hot weather forecast for the next week residents need to be particularly careful with water use. Irrigation of gardens should only take place in the early morning and later evening to avoid the heat of the day. Desirably water use should be kept below 3500 cubic metres per day and the output from the pump station not exceed 55 litres per second. The graphs show these outputs over the last week.
On Sunday evening water demand in Renwick exceeded 55 litres per second. This caused the reservoir level to fall to 30%. This is about the absolute minimum which needs to be retained for firefighting purposes. What does this mean?? Renwick’s water demand on Sunday is the maximum the system can meet. When considering voluntary water limits residents should be aware to not contribute to a water demand which creates the water output from the water treatment plant to exceed 55 litres per second.
How do I know if I should irrigate?
Throughout this week we will publish an alert on this web site to show if and when this limit is exceeded. We will also publish this notification on the Antenno app. We would then encourage residents to look for this information during very hot afternoons before they commence irrigating or not.
Water Saving Tips
What is the Renwick Aquifer level graph showing?
This graph shows the aquifer level at Well 3 in Terrace Road for this year (red line) compared to last year (blue line). The water level is measured in millimetres above the top of the pump in the well. The green line across the page at 1,000 mm is the minimum level the well has to be at to protect the pump from being damaged by air which can be drawn into the pump when the water level is close to the pump intake.
Reducing the pump's output will elevate the aquifer level at the well when the pump is running. But when the output from the wells is reduced, the volume of water available to Renwick is also reduced. At these times it is necessary for the community to reduce peak water demand. The demand has to be approximately equal to or less than the combined output from the bore pumps. This is normally about 55 litres per second.
The reduction can be voluntary or with the implementation of restrictions.
This graph also shows the water used daily (purple line).
What does the reservoir versus demand show?
The reservoir level is shown with the blue line and water demand by the red line (in litres per second).
During normal demand the reservoir fills and empties in the range of 85% to 98 %. It fills when the well pumps are operating, providing 50 to 60 litres per second. This input flow is generally in excess of demand so the reservoir fills. If demand exceeds the input from the wells, the reservoir will continue to empty beyond the well pump start level of 85% until demand drops back below the output rate from the wells.
History of Renwick's water supply
The public water supply to Renwick was first established in 1975. Water was abstracted from a well in Terrace Road and pumped to a storage reservoir at an elevated site close to Boyce Street, now in River Terrace. After basic treatment, the water was pumped into supply. Since then, two further bores have been installed and a tank farm of nine storage tanks added to the Boyce Street site. The water is aerated through a trickle aerator on the way to the tanks. The water is disinfected with chlorine before being pumped to the township.
The water does not meet the protozoal requirements of the Drinking-water Standards for New Zealand (DWSNZ).
Flow and pressure are monitored at the treatment/pump station and the two distribution pumps are automatically started and stopped to meet demand fluctuations. Around half of the reticulation is asbestos cement pipe; the remainder is split evenly between polyethylene and PVC.
Water demand varies from summer to winter. During the winter demand is generally 1,500 cubic metres per day, however; during summer this can increase to 3,500 cubic metres per day. Most of this increase is due to irrigation of gardens and lawns.
During recent summers, water restrictions have had to be implemented to reduce demand as the water level at the wells has fallen. When levels get too low and recharge cannot keep up with demand the volume of water that can be extracted has to be reduced. It’s during these times there are water restrictions.
The following extract and minor additions help explain why there is a need for water restrictions; it is taken from the flyer produced by Renwick’s Smart and Connected Water Working Group.
Renwick Smart and Connected Water Group - water information from flyer
Last summer, there were many rumours about why we ran low on water. The group investigated the truth about Renwick’s water supply.
The following information will dispel some of those myths and give you a greater insight into why we face water restrictions in the summer.
- The positioning of the three Renwick township wells was decided on for economic and practical grounds when the system was set up in the 1970s and has served the community well.
- The original water supply for Renwick was designed for a smaller population with smaller landscaped gardens and the wells can no longer cope with the demand in times of high summer use.
- We live in a ‘thirsty’ area due to the type of soil and climatic conditions (low rainfall, high sun and drying winds). Garden irrigation is by far the biggest draw on water for urban Renwick during the summer months, with approximately 70% of peak day water use being for this purpose.
- The wells cannot recharge at a fast enough rate to keep up with this demand.
- It is this slow recharge rate that is the primary problem rather than any issue with the aquifer itself, or the result of others using the water (e.g. vineyards, Blenheim, Woodbourne etc).
- The wells are at the edge of the Wairau Aquifer and the soils there are not as free flowing as those closer to the river. They have been drilled to the maximum possible depth and cannot be made more productive.
- Localised rainfall does not recharge the aquifer; it is the Wairau River (and Gibsons Creek) that recharges the aquifer
- As is common in older water supply networks, some water is lost from leaks in the Renwick water supply system. Council began a programme of work in 2014 to locate and repair leaks at the roadside and on private properties. This work is ongoing.
- There are three new wells on Conders Bend Road, which are closer to the river and expected to have a faster recharge rate than the current wells. Tests are being undertaken by Council to confirm this.
What’s being done to address the summer water supply problem? Testing of new bores in Conders Bend Road was completed during the winter of 2016. The testing was necessary to prove the yields from the well are going to meet current and future demand. On completion of satisfactory testing, Council will apply for resource consent to use the water for Renwick urban water supply. The construction of a pipeline and pumping infrastructure to provide this new water to the Renwick Community is programmed for 2018/19.
In the meantime it will be necessary to implement water restrictions over summer when the current wells are unable to meet demand.
Use of asbestos cement pipe in water supplies
Asbestos cement pipes were used around the world for providing drinking water during the 1980s and 1990s.
There have been numerous studies to show there are no health issues associated with the use of this pipe for carrying drinking water. Their use has since been discontinued for a variety of reasons, including the fact that they fracture with earth movements such as earthquakes. Human health impacts only occur if asbestos fibre dust is inhaled directly into the lungs.
See the World Health Organisation Report on asbestos in drinking water:
Marlborough District Council is replacing these pipes in Renwick and elsewhere as they age, or when repairing leaks becomes uneconomic.
Fees and forms
See information on charges:
Apply for connection or disconnection application forms:
Information on water meter trials in Renwick.