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Keeping our drinking water safe

​​Secure groundwater

In 2003, Council made the decision to upgrade our water supplies to make sure that our drinking water is safe, reliable and sustainable.

A major part of upgrading our supplies was drilling new deep groundwater bores (wells) that are secure. This means that the water in these bores come​s from an aquifer deep enough underground that it is not affected by what happens on the ground surface or by the weather.  The top of the well (or borehead) is also designed to stop contamination of the water in the aquifer.

Below is a table that shows the water supplies that are supplied by deep groundwater, and the depths of the bores. Some of the bores have links to photos.

​Water Supply​Bore Name​Bore Depth
​Ashburton ​ ​ ​ ​ ​ ​ ​Argyle Park #1*​96m
​Argyle Park #2*​91m
Ashburton Domain #5*​96m
Ashburton Domain #691m
​Ashburton Domain #7​113m
​Bridge Street #1*​95m
Bridge Street #2*​99m
​Tinwald Domain​74m
​Rakaia​Rakaia Bore​117m
​Fairton​Fairton Bore​101m
​Hinds​Hinds Bore*​102m
​MayfieldMayfield Bore*​119m
​Chertsey​Chertsey Bore*​145m
​Dromore​Dromore Bore*​102m

As part of the ongoing impact of the Havelock North Inquiry findings, water supply sources are now being assessed with greater scrutiny nationwide, which has resulted in many councils’ water supplies losing secure status. Bores in Ashburton District which currently do not have full secure status are indicated with an asterisk (*). The revoked status does not pose any significant changes for residents and no contaminants have been detected.

We are continuing to treat the water as we have done for many years as a safety measure and are now conducting more frequent water tests as required. Minor improvements have been made already, and work is in the pipeline to restore full secure status and to apply additional treatment to the water.

The other Council water supplies get their water from bores, infiltration galleries, or from streams. These sources can be affected by what happens on the surface or by the weather, so the water needs extra treatment to make sure that it is safe to drink.

In the last few years we have upgraded the treatment at Methven, Mt Somers and Hakatere. Montalto and Methven Springfield are in the planning stage.

Treating the water to keep it safe

The treatment on the different water supplies is shown in this table:

Water SupplyWater SourceTreatment
AshburtonSecure groundwaterChlorination, pH correction
MethvenInfiltration galleryChlorination, filtration, UV disinfection
RakaiaSecure groundwaterChlorination
FairtonSecure groundwaterChlorination
HakatereGroundwaterChlorination, iron and manganese removal, UV disinfection
HindsSecure groundwaterChlorination
MayfieldSecure groundwaterChlorination
ChertseySecure groundwaterChlorination
Mt SomersInfiltration galleryChlorination, filtration, UV disinfection
DromoreSecure groundwaterChlorination
Methven SpringfieldInfiltration galleryChlorination, UV disinfection
MontaltoSurface waterChlorination, UV disinfection

All Council water supplies are chlorinated fulltime. This is done, even on secure groundwater supplies, to kill any bacteria that might be introduced into the water supply after it leaves the treatment plant (e.g. at a break in a pipe). Chlorination is excellent at killing harmful bacteria such as E. coli and Campylobacter.

Filtration and UV disinfection are used where the source is not secure groundwater. These sources can be affected by what happens on the surface or by the weather, so the water needs extra treatment to make sure it is safe to drink.

Checking that the water is safe

Water is regularly tested and sampled to confirm the safety and quality of the water we supply to our customers.  We look for a number of different things, including:

  • E. coli, to spot any possible contamination
  • FAC (chlorine), pH and turbidity to check that chlorination is working correctly
  • Nitrate, to look for any trends and ensure levels are completely safe
  • Water chemistry, looking for any other potentially harmful chemicals

The Ashburton, Methven and Rakaia treatment plants have automatic chlorine monitors checking the levels of disinfectant at all times. E. coli, chemical sampling is carried out on a schedule determined by the Drinking Water Standards. We also carry out optional sampling, above and beyond the requirements.

Our sampling process usually involves the following steps:

  • Water samples are taken from sample points on the supplies
  • Samples are analysed at Council's laboratory to see if the bacteria E. coli is present or not
  • Samples that need analysis for other chemicals or metals are sent to another specialist laboratory

Council's laboratory has Ministry of Health recognition to do E. coli analysis and is independently audited every year.

If E. coli is found in the water the following steps are undertaken:

  • The public health authorities at Community and Public Health are notified
  • Contractors investigate what caused the problem and fix it
  • More sampling is undertaken until there are three days with no E. coli in the samples
  • Where necessary, and upon the advice of health authorities, a boil water notice may be issued

Planning for the future

All of the Council water supplies have a current Water Safety Plan (WSP) in place. These plans explain how we keep the water safe and minimise the chance of anything going wrong. WSPs are agreed with the Ministry of Health, and show that we're working together to improve water quality.

Current Water Safety Plans​
​Mt Somers​Dromore

WSPs also talk about how we plan to improve the supplies even further. Examples of possible improvements include:

  • Any new, replacement or upgraded treatment equipment required to meet the Drinking Water Standards
  • Extra monitoring and alarms to spot any problems sooner
  • Updating our plans for incident response so supplies can be resilient.