Contamination Issue at Havelock North - a Laboratory Perspective
In light of the water contamination issue in Havelock North, members of the public are questioning whether the drinking water testing programme in New Zealand is appropriate and if that programme is sufficiently managing the risks of water contamination. At the time of writing this newsletter an investigation is underway to identify the source of the contamination.
Drinking water testing in New Zealand follows the “Drinking-water Standards for New Zealand 2005 (Revised 2008)” or NZDWS, a document that can be found on the Ministry of Health website. The document was put together by people with technical expertise in local and national legislation, water treatment, statistics and laboratory analysis, and also with consultative input from the public.
The standard sets out legally binding procedures that suppliers of drinking water to communities of more than 500 people must follow.
The question, Is our reticulated drinking water safe? can be answered Yes, for communities who have the NZDWS structure in place, and for those who have factored and controlled all of the risks documented in their Water Safety Plan. Clearly something has happened in Havelock North that is not covered by the NZDWS and the councils Water Safety Plan.
Finding the answer to this contamination event is essential for the whole of New Zealand to understand and learn from.
So what laboratory testing processes are in place for our drinking water supplies?
A typical water supply consists of three parts: The source, The Treatment Plant and The Distribution. Each part of this network is closely monitored through microbiological, protozoal and chemical testing by an IANZ accredited laboratory.
The results of this testing are entered into the National Water Information New Zealand (WINZ) database and are used to measure compliance against the NZDWS. Compliance is reviewed by Drinking Water Assessors (DWA’s) who work for Ministry of Health.
The ministry for the environment website shows the graphic on the next page which describes a community water supply in drinking standards terminology. All of the communities in New Zealand receive water through the same network of Source, Treatment Plant and Distribution. Auckland and Wellington also have an extra stage called ‘Bulk Network” which sits between the Treatment Plant and the Distribution system.
Source – WINZ Prefix is S0 or G0
The source of a water supply is varied and can be:
- A lake such as Lake Wakatipu in Central Otago (WINZ Code S00062),
- A river such as the Waikato River (various WINZ Codes such as S00865 for Auckland,
S00041 for Hamilton or S00070 for Ngaruawahia) or the Waiwhakaiho River in New
Plymouth (WINZ Code S00233)
- Streams and Creeks such as the Kaipatangata Stream in Carterton (WINZ Code S00591) or Deep Creek in Dunedin (WINZ Code S00999)
- A large number of water supplies are sourced by bores or groundwater such as the Wharawhara Bore in Katikati (WINZ Code G01610) or Mahoe Street Well in Lower Hutt (WINZ Code G00445). Within the drinking water standards is a process to prove the groundwater is secure and unaffected by surface contamination.
- Tankered water carriers are required to be registered and also have their own WINZ codes such as Flanders Waterpower Ltd in the Hawkes Bay – WINZ Code WC00210
- At present there are no desalination plants operating in New Zealand but these could in the future become drinking water sources.
Treatment Plant – WINZ Prefix is TP
Many of us would think that a treatment plant would be a large building containing a complicated process. However, treatment Plants are surprisingly varied and can be as simple as a chlorine dosing machine or as complicated as the multi-million dollar facility with flocculation, membrane filtration and disinfection that we all envisage. All treatment plants are shown in the WINZ database with the prefix TP.
Zone or Distribution– WINZ Prefix is varied
A zone is a defined area where the water is consumed. Like all other parts of the network these zones are variable and range in geographical size and population with zones with a few as 100 people (Haywards Zone in Lower Hutt with 372 people - LOW001HA) to over 100,000 (Auckland Zone with 261,638 people - AUC003AU). Most cities and town have multiple zones based on the pipes distributing water to those areas. In the latest Ministry of Health Annual report on Drinking Water Quality there were 660 zones reported. These 660 zones represent 3,787,000 New Zealand drinking water consumers.
What can cause a positive E.coli result in a drinking water sample?
In the past few weeks councils around New Zealand have announced that they have recorded positive E. coli results in their drinking water zones. Christchurch City Council has reported 14 positive results, MacKenzie District Council has recorded 7, while Timaru District Council has recorded just one.
It is possible that some of these positive results were not from the water. There are many things that can cause a positive E. coli result, including the water itself. Over the years, Eurofins-ELS has attributed the following to some of our positive E. coli results. It is essential to remember that whenever a positive E. coli is recorded that it must be treated as a real contamination.
Sampling conditions: Was the sample tap sterilised adequately? Was it raining, extremely windy and did contaminated water drip from overhead into the sample container? Were the sampler’s hands and equipment clean?
Sample Point Selection: Is the sample point suitable? Some sample taps are close to the ground and can get contaminated by soil, so selecting the correct sample location is essential. Never collect a sample through a garden hose!
Sample Point Selection: Has the sample point been contaminated? Here at Eurofins-ELS we have witnessed sample point contamination from dogs as well as cows. In one incident we kept recording positive E. coli results from a tap attached to the outside of a domestic house. The tap inside, as well as all other taps in the area were always negative, and we couldn’t work out why.
After several days of repeat analysis our sampler noticed that the household dog was licking the tap, and even though we sterilise the taps before sampling, this clearly wasn’t sufficient to remove the contamination caused by the dog’s mouth.
Low Level Contamination: Some reservoirs may have a very low level of contamination which is not identified in the 100mL sample that is collected for laboratory analysis. For example, if the contamination is present at 1 organism per litre then statistically we would only record a positive with every tenth sample.
Shipping Conditions: The samples need to be transported to an IANZ accredited laboratory for testing. It is therefore very important to ensure that the container the samples are transported in is very clean. We have seen incidents where drinking water samples have been carried with effluent and environmental samples and this can lead to cross contamination.
Cleanliness of the whole shipping container is essential and needs to include any devices used to chill the sample. This includes solid ‘slikka’ pads which must be cleaned if they have been used for transporting any other non-potable water samples.
Sample bottles must be free from cracks or defects or they could leak in transit.
Finally, it is important to note the effect of the icepacks used in transit and what the cooling and heating does to the sample containers. The shrinking and expansion of the plastic can lead to leaking so it is important for the sampler to ensure the lids are tightly sealed before sending them off to the laboratory.
False Positives: Even if everything proceeds without any external contamination of the sample there is still the possibility that the test itself returns a false positive. The test itself is known to falsely report some samples as positives even when they do not contain E. coli. The rate is very low, but for major labs such as Eurofins-ELS who perform over 20,000 drinking water analysis per annum, there will be incidents where one or two samples will be reported as false positive.
The test process can sometimes be tricked into reporting false positives by other bacterial species such as aeromonas1if they are present in the water sample at sufficient numbers.
1 A Comparison of Ten USEPA-Approved Enzyme-Based Total Coliform/E. coli Tests for Microbiological Groundwater Monitoring and Laboratory Consultation. James Jay Schauer, Ph.D., PE; Jeremy Olstadt; Jon Standridge , Sharon Kluender
Contamination Issues Around New Zealand
The Havelock North water supply is non-chlorinated because, like a handful of other supplies around New Zealand has its water sourced from a borefield categorised as secure. Other non-chlorinated water supplies around New Zealand include Arrowtown, Christchurch and the Hutt Valley. Residents of these locations prefer their water to be non-chlorinated and actively entreat their local councils to maintain this status.
The population of Arrowtown in Central Otago has a history of contamination incidents. E. coli outbreaks in 2010, 2013, 2014 and twice in 2015, which have all lead to boil water notices and temporary chlorination. The population still wishes its water supply to remain non-chlorinated.
Havelock North also has experienced previous contamination outbreaks. In 1998 the water supply was contaminated leading to a large water related campylobacter outbreak. Like the most recent incident, this 1998 outbreak was linked to Brookvale Rd bore No.2.
Brookvale Rd bore No:2
The 1998 outbreak was most likely caused by contaminated surface water entering the well at the above-ground level point where the bore is located. This is known as an insecure bore-head and does not mean that the water in the underground aquifer is contaminated. The Hastings District Council is currently investigating whether the two contamination outbreaks have a related cause.
In similar contamination cases around New Zealand, an engineering fix such as installing a sump pump or leak-proofing the above-ground structure is all that’s required to remove the ongoing contamination issue. Where large above-ground concrete reservoirs have been contaminated, the fix has included sealing cracks caused by earthquakes or tree-roots. Sometimes, further equipment is installed such as UV treatment.
But at the end of the day, a water supply that does not carry a residual level of chlorine throughout its reticulation, does not have the capacity to kill contamination that can enter at any point. A nonchlorinated network requires not just a secure water supply, but a secure water delivery system right up until the consumers tap. If at any point this fails, then contamination can enter and spread.
There are two very important questions that will need to be answered – What was the root cause of the outbreak in Havelock North? And should chlorination of water supplies become mandatory?
The answers to both of these answers could lead to a major change in the way councils deliver our drinking water.
