Martinborough water supply - towards resilience

This summer we’re planning to install a manganese extraction plant to progress towards permanent chlorination of the Martinborough town water supply. The current chlorination arrangements are temporary because the town is being supplied by only one bore, the one with the lowest levels of manganese. Water with high levels of manganese becomes discoloured when chlorine is added.

Effectively removing the manganese from the town water supply and being able to return to drawing water from more than one bore is the best course of action to ensure clean, clear, safe and secure water for the town.

Why our current arrangements are temporary

A temporary arrangement is in place now where water is being supplied, from the bore with the lowest manganese levels, to supply the Martinborough township. Water quality has not been an issue to date because the manganese levels are suitably low not to react with chlorine and discolour the water.

However, the current situation is temporary for a number of reasons – with one bore in use:

  • there are maintenance issues - doing work will interrupt supply and the system is vulnerable to mechanical breakdowns.
  • water demand will likely exceed supply in the summer months.

We are committed to permanent chlorination of the water

Urgent action is being taken to ensure the sustained delivery of clean, clear and safe and secure drinking water for the community. The naturally occurring manganese in the town’s water supply can block filters and when mixed with chlorine causes discolouration.

We’re going to fix this problem with the installation of a manganese extraction plant. This will enable water to be supplied and chlorinated from all the bores. Taking the manganese out of the water supply completely also means that water filters will no longer get blocked with manganese as they do now.

The plan is for the manganese extraction plant to be operational by early summer.

How the manganese extraction plant is being paid for

The manganese extraction plant is primarily loan funded with the remainder coming from the Martinborough infrastructure reserve. This means that the cost of the manganese plant will be achieved within the Annual Plan budgets, with the 5.48% increase remaining the same. 

What about drilling other bores without manganese in them rather than going straight to manganese extraction?

There is no guarantee that drilling a new bore will have low manganese. Council tested a private bore close to a public supply bore and found that it had very high concentrations of manganese, as well as iron.

This is because manganese is a transition metal and is a naturally occurring element in the greywacke sandstone gravels of the river plain.

Manganese and iron are to an extent water soluble. This means that when water runs over them they may dissolve out of the gravels and travel along with the water. The longer groundwater spends sitting in an acquifer made of greywacke gravels, the more of these dissolved metals it can contain.

The water that contains these dissolved minerals is pulled up to the surface via a bore. As the water is pulled from the ground, it’s acidity (PH) and level of oxygenation can change, and this in turn can result in dissolved Manganese and iron to reform as solid sediment which can clog filters and sits in the bottom of pipes.

Recent history – why is the water in Martinborough being temporarily chlorinated?

To ensure that the Martinborough town water supply is safe to drink. The source of the E.coli could not be found in April/May when the boil water notice was issued by Regional Public Health. Temporary chlorination was required in order for the boil water notice to be lifted.

Following the recommendations post the Havelock North water incident, we have been moving towards a multi-barrier approach in the delivery of clean, clear, safe and secure drinking water. With this in place, boil water notices will be a thing of the past.

More background information.

Managing water supply, before the manganese extraction plant is installed

When the manganese extraction plant is operational, bores with higher manganese levels will be back in use. This means that things will be back to normal from a water supply perspective.

In the meantime, everyone has a part to play in managing summer water demand. Usually, in the summer months the community can expect outdoor watering restrictions in January or February. These water restrictions are linked to flow in the Ruamahanga River.

However, this year we’ll need to carefully monitor water consumption and put water restrictions in place if consumption goes above 1,200m³/day. Practically, this means that:

  • when the summer weather begins it’s likely that water restrictions/sprinkler ban could be applied earlier than usual
  • we will keep the community informed about water consumption levels
  • people can expect one week’s notice before a sprinkler ban is put in place
  • now is an excellent time to voluntarily conserve water.

As it nears summer, it it prposed that the town's water consumption will be reported on our website every second day. Water consumption will be categorised:

  • Green – less than 1200m³/day
  • Amber – between 1200 m³/ and 1600m³/day – water restrictions: sprinkler ban
  • Red – over 1600m³/day – water restrictions: hose pipe ban.

Living with permanent chlorination of Martinborough's water 

 

Why is chlorine the best choice?

Chlorination is the most widely used method of water supply network disinfection in the world, and its levels are closely monitored to be within the limits recommended in water quality standards. It provides a critical water safety barrier to ensure customers who are connected to the water supply network are protected from illness should contamination of the water ever occur.

Does chlorination impact and corrode pipework and water cylinders?

Corrosion of metallic fittings used in conveying or storing water (including copper hot water cylinders) can be caused by many factors – including the quality of manufacture and composition of the material, soil type (when underground) and water chemistry.

Treatment processes can be used to minimise corrosion caused by water quality as reflected in the pH and alkalinity of the water that leaves the treatment plant. However, because of the complexity of metal corrosion mechanisms it cannot guarantee elimination of corrosion of pipes, pipe fittings and storage vessels.

How can I get rid of the chlorine taste?

If the faint taste of chlorine bothers you, there are a couple of tricks you can use to help reduce the taste of chlorine in your drinking water. You can put the water in a container or jug in the fridge (over time the chlorine level in the water decreases) for around 48 hours or boil it. You may find that using a water filter that uses carbon filtration helps (please consult the manufacturer's instructions on recommended use).

Chlorine and infant formula

Chlorinated tap water is considered safe for babies who require formula feeding. If parents are concerned by the smell or taste of chlorinated water it can be left to stand in a jug in the fridge and the chlorine will dissipate (leave) within hours. All water used to make up infant formula should be boiled and then cooled as per Ministry of Health guidelines and further chlorine will be removed in this way.

What about my pet fish?

If you have fish outside in ponds you will need to either turn down in-coming water to an absolute trickle (this dilutes the chlorine level to a safe amount for your fish), or fill up drums of water and let them stand for at least 24-hours before using (the UV of the sun evaporates chlorine). For fish tanks or bowls inside, fill up a container of water and let it sit for at least 24-hours and then only replace 1/3 of this water at a time with what is in the tank already. If you’re still worried, de-chlorinating kits can be purchased from pet stores.

What does it mean for my water softener?

Please refer to the recommendations of the manufacturer regarding water softeners and chlorinated water. It’s possible that the filter will need to be changed/cleaned more frequently.

Questions and feeback

If you have any questions or feedback about this project, please contact us by emailing martinboroughwater@swdc.govt.nz.

Chief Executive Harry Wilson will be available to discuss this topic throughout the day on 22 August, and in the evenings on request. Please contact Barbara Gavan on 06 306 9611 ex. 832 to book a meeting.

 

South Wairarapa District Council