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Water Chlorination

General Information

1) What's this all about?

The draft Long Term Plan 2018-28 includes a proposal to chlorinate the Geraldine and Pleasant Point urban water supplies (GWS and PPWS). These supplies are currently unchlorinated, which does expose the consumers of this water to risk if the water supplies were contaminated somehow.

Providing budget for chlorination does not pre-determine the outcome of the consultation; it simply ensures that the funds are available to chlorinate if that is what the Council decides following the consultation.

All other urban water supplies in the Timaru District are currently chlorinated.

2) Why is this proposed?

Ultimately, this is about safe drinking water. Supplying drinking water that is safe and clean is one of TDC's key responsibilities. There is a community expectation and legal requirement that the water for residents and visitors is safe to drink.

Under the Health Act, we are legally required to provide a safe and wholesome drinking water supply and do everything practicable to meet the Drinking Water Standards for New Zealand. Any change in the law going forward will likely strengthen this requirement.

While the water is currently treated, chlorination provides a residual that will manage contamination events within the reticulation. A residual means that a very small amount of chlorine remains in the water to deal with potential contamination events. Examples of the causes of recontamination could be backflow from a private property back into the reticulation, such as with maintenance on the plumbing within the house, or an incident where the reticulation is damaged, or where contamination might occur while maintaining the reticulation.

TDC is obligated to learn from the Havelock North experience, where a serious contamination event occurred in 2016. This caused a major outbreak of campylobacter and resulted in over 5,000 people getting sick. The main reason for this contamination has been identified as contamination from the source, no treatment processes and ineffective barriers to contamination.

Saying that it would not happen here is no excuse for not using chlorination. It can and has happened in other areas.

3) What was the Havelock North Drinking Water Inquiry? Why is the TDC using it to justify the GWS and PPWS being chlorinated?

As a result of the Havelock North event, the government initiated the Havelock North Drinking Water Inquiry with the final December 2017 report outlining a number of recommendations for drinking water supplies. The commissioners have thoroughly researched both the cause of the Havelock North issue and water management throughout NZ.

They have recommended to government and all water suppliers that there should be a residual disinfection within the water reticulation. Chlorine provides a residual disinfection, and effectively a safeguard against potential contamination.

As a supplier of water, Council needs to consider multiple barriers to prevent contamination and ensure water remains safe.

Final decisions are expected from the government soon.

4) Is chlorination effective against campylobacter?

Chlorination offers residual protection against a wide range of bacteria including eColi and Campylobacter (which was the bacteria that caused the problem in Havelock North). It ensures that any bacteria that enters the system after the initial treatment is killed.

5) Why have Geraldine and Pleasant Point water supplies never been chlorinated previously?

These supplies are treated to Drinking Water Standards for New Zealand, but this does not provide the protection against potential contamination that chlorination would provide.

6) So is our water currently safe?

All of our water treatment plants comply with the Drinking Water Standards for New Zealand (DWSNZ) for bacteria. This includes Geraldine and Pleasant Point. Five of our rural water supply schemes do not currently meet protozoal (giardia and cryptosporidium) compliance, however these will be upgraded or removed from service by 2021.

Rigorous testing regimes apply to our drinking water supplies. Water is sampled for bacteria by our operators and tested at Medlab South, an approved laboratory. The number of samples taken is 50% greater than the DSWNZ require. For protozoal compliance a number of parameters are automatically measured and recorded every minute. UV plants are monitored continually.

7) What is chlorination? What does it do when it is added to a water supply?

Water chlorination is the process of adding chlorine (Cl2) to water. It is used to kill bacteria and other microbes, and prevent the spread of waterborne diseases such as cholera, dysentery and typhoid. Chlorination provides an extra layer of protection against these waterborne diseases.

8) Why is chlorination the preferred treatment of choice?

Chlorination provides an additional treatment barrier within the water reticulation. Chlorination is cost-effective, reliable and easily implemented and substantially raises the level of protection of the water supply. Currently, it is used for all other urban water supplies and has been used internationally for over 120 years. Any other options chosen would need to be as effective and affordable as chlorine. If a more expensive alternative option was chosen, the community would have to consider where the costs of that choice would fall. Alternatively, if these options are more cost effective in the future, they could be reconsidered.

9) Does chlorination affect the taste of the water?

There may be some minor taste implications, but you do have choices.

  • Fill a jug of water and leave it on the bench or in your fridge overnight. The chlorine will dissipate naturally over a few hours.
  • Install a carbon filter

10) How can water backflow into any water network occur?

Backflow occurs when there is greater pressure on the private property side of a water connection than the pressure in the water main. This can occur if there is a pressure drop in the reticulation, such as when the main is emptied for repair, or if there is a pump on the private property. Backflow is when water flows in the reverse direction (i.e. from the private property back to the main), and this water could be contaminated. It is extremely hard to detect and many commercial properties are required to have backflow prevention devices fitted to reduce the risk.

11) Does chlorination impact on people's health if they drink the water?

No. Chlorine has been used safely all over the world for around 120 years. It keeps millions of people all round the world – including most of New Zealand – safe from waterborne illness.

12) How much chlorine is used to chlorinate a water supply?

As little chlorine as possible is used to keep your water safe. Approximately 0.5 - 1.0 ml of liquid chlorine per bucket of water.

Typically we will use a dose of 0.5mg of chlorine for every litre of water. This will give a residual dose of 0.2mg per litre in what comes through your taps.

13) What about the long term effects?

Under the drinking water standards and based on current knowledge, you can only use treatment that will constitute no significant risk to the health of a person who consumes 2 litres of water a day over their lifetime (which is averaged out to around 70 years).

13) Is the chlorination proposed to be permanent?

Currently, it is proposed to be a permanent solution.

14) Will chlorination affect my pets?

No, except water for a fish tank may need to be neutralised. (see answer 9)

15) Isn't chlorine toxic?

Not in the concentration that is used for disinfection as described above.

Further reading

Geraldine Water Supply (GWS):

1) What are the current Water Treatment processes for the Geraldine Water Supply (GWS) and Pleasant Point Water Supply (PPWS)?

Shallow ground water is treated by Ultra Violet irradiation. This treats the water at the source by inactivating bacteria, virus and protozoa.

UV (ultra violet light) treats the water where it enters our supply network. It is very effective as long as the water is not turbid (discoloured). UV treatment has no residual as compared to chlorination and does not provide further protection against contamination of the water once it is in our reservoirs and pipes.

There is always the potential for contaminants to get into the water reticulation system, for example through broken pipes or backflow.

2) For what reason is the Timaru District Council (TDC) proposing to chlorinate the Geraldine Water Supply?

To minimise the risk of recontamination of the treated water within the reticulation. Examples of the causes of recontamination could be backflow from a private property back into the reticulation, such as with maintenance on the plumbing within the house, or an incident where the reticulation is damaged, or where contamination might occur while maintaining the reticulation.

3) Has there ever been a contamination issue with the Geraldine bore field, and if yes what was the cause?

In July 2018, flooding allowed surface water to enter the treatment plant. This water was turbid (slightly discoloured but not visually) and resulted in non-compliance with the Drinking Water Standards for NZ (DWSNZ) for 15 minutes.

4a) How often is the GWS tested at the bore head?

Monthly for bacteria and nitrates.

4b) How often is the GWS tested at the Reservoir?

When contamination is found within the reticulation.

4c) How often is the GWS tested at the reticulation?

Three (3) samples per fortnight

5) Has there ever been an issue with the GWS distribution network?

In 2017, there were 2 samples taken within the reticulation that detected the presence of bacteria. The source of contamination was within the reticulation but never found. Chlorine was added to the water at the source to eliminate the contamination.

6) What is the cost to urban water ratepayers to chlorinate the GWS?

Less than $2.00 per household per annum.

7) What type of chlorine is proposed to be used to chlorinate the GWS?

On site generation of sodium hypochlorite, which is a liquid form of chlorine.

8) Council has chlorinated the GWS after heavy rain events in the past. Why can’t the status quo be kept?

This statement is not correct, Council has not necessarily chlorinated after heavy rain events. Council has chlorinated the GWS after contamination events in the past.

As noted in 4c), 3 water samples are taken from the reticulation on 2 days in every two week period. In fact this sampling regime is 50% more than that required by DWSNZ, which itself aims to give 95% confidence that the supply complies with DWSNZ 95% of the time. There is a risk that a contamination event could go undetected.

9) Has backflow ever happened in the GWS?

We are aware of an incident when a water main was shut off to repair a pipe and a consumer who had left a hose running on the compost bin had an internal backflow event that resulted in grass discharging from the kitchen tap.

It is unlikely that TDC would be advised, or that the premises might even be aware that a backflow would be occurring.

10) Does council have a safety plan ready for when a water network back flow event occurs?

The Geraldine Water Safety plan details the actions required when a backflow event is detected.

Have your say?

Click here to have your say about this and any other LTP issues. Use the Other Feedback section if you wish to comment about chlorination.

Publish Date: 23 Mar 2018