Renwick Water Supply and Reticulation

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Renwick Water Supply and Reticulation

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Renwick water supply updates

Despite the hot, dry weather Renwick residents have started off the summer as they finished last year, conserving water and irrigating efficiently. Water demand has been kept below the sustainable level of 3,000 cubic metres per day, only exceeding late last week when the weather was very hot.

“Residents are to be congratulated. If they keep this up during the summer again as they did last year, water restrictions should not be necessary,” says Council’s Operations and Maintenance Engineer Stephen Rooney.

“We’re asking Renwick people to think about their water use again this summer. We avoided hosing restrictions last summer and we hope we won’t need them this year either,”

The aquifer water level at Renwick isn’t looking as healthy compared to this time last year, but it is still much better than it was leading into the summer of 2015/16.

The Wairau River, the source of the aquifer recharge, is starting to get low, flowing at only an average of 26.5 cubic metres per second over the weekend. This is much lower than the average of 80m3/s during December last year. A good spell of rain is needed to sustain river flows and aquifer recharge.

Council is again publishing graphs showing the aquifer water level at the Renwick bores in relation to demand. Residents can keep a watch on the township’s water consumption (see below).

Meanwhile, the testing of new wells at Conders Bend Road is complete. Council is expecting reports from the consulting engineers in the next few weeks. These wells are intended to provide the future domestic water supply for Renwick.

Renwick’s new reservoir is scheduled to be in place this financial year (2017/2018) and the new water supply and treatment plant upgrade the following year, 2018/2019.

Water saving tips to achieve water savings in and around the household

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.

Water restrictions

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.

Next steps

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:

Go to World Health Organisation Report

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:

Connection and disconnection fees

Apply for connection or disconnection application forms:

Connection or disconnection application forms

Other Information

Compliance with Drinking Water Standards NZ

Chemical Analysis Reports