Mahuta’s Three Waters law was promoted as a health measure as well as a cost-saver – but whose figures should we use?

After the Water Services Entities Bill passed its third reading in Parliament, Local Government Minister Nanaia Mahuta said it was the first of three bills that will ensure affordable drinking water, wastewater and stormwater services can be provided to New Zealanders now and into the future.

Everyone agreed that change was needed to ensure communities have safe, reliable drinking water at an affordable price, she said.

“We are already seeing what is at stake with over 34,000 New Zealanders getting sick from drinking water each year.”

Point of Order has been dipping into the most recent data we could find on the Massey University-based Environmental Health Intelligence NZ website.

This provides information and intelligence on how the environment affects the health of New Zealand’s population.

We focused on a factsheet (dated May this year) headed Notifications of potentially waterborne diseases.

The factsheet says it presents information on how New Zealanders’ health is affected by three potentially waterborne diseases: campylobacteriosis, giardiasis and cryptosporidiosis.

It acknowledged that low recorded notification rates of the three common potentially waterborne diseases in 2020 may be due to reduced access to healthcare caused by the coronavirus pandemic.

The key findings were:

•  The age-standardised rate of campylobacteriosis notifications was 101.5 per 100,000 people in 2020, the lowest rate since the start of records in 2001.   
• The notification rate for cryptosporidiosis was 17.3 per 100,000 people, one of the lowest reported rates since 2001.
• There was a sharp drop in the notification rate for giardiasis from 2019 (34.3 per 100,000) to 2020 (22.5 per 100,000 people. The sudden significant change is likely to reflect the impact of Covid-19 rather than a difference in the actual rate of disease.

The notifications presented in the report cover only people who sought medical treatment. Therefore any difference in notification rates between 2019 and 2020 may be partly due to more people being unable or unwilling to access healthcare during periods of heightened COVID-19 restrictions.

The report further acknowledged the possibility that COVID-19 restrictions will have caused a genuine reduction in cases, in particular those connected to recreational activity.

The reduced access to healthcare coupled with the already imperfect collection of risk factor information (see the factsheets relating notifications of waterborne disease with untreated water and recreational water contact as risk factors) are likely to disguise the extent of this effect.

For this reason, readers should be aware that rates are presented ‘as is’ and use caution when interpreting the graphs shown below.

Campylobacteriosis notification rate, 2001–2020   

The campylobacteriosis notification rate in 2020 was 101.5 per 100,000 people (5,226 notifications), the lowest since reports began in 2001 and continuing a declining trend from 2009 onwards.

“The minor elevation” in the rate for 2016 was due to a campylobacteriosis outbreak in Havelock North, the report says.

This is the outbreak which loomed large in the Government’s attempts to scare the country into recognising the need for the Three Waters programme. 

TV One last week reported:

The [Three Waters] legislation was introduced after the Havelock North disaster in 2016 when 8000 people became sick, and eight died because of contaminated drinking water – out-of-date water infrastructure played a major part in the crisis.

This amplifies the figure contained in the official report into the crisis:  

The outbreak of gastroenteritis in Havelock North in August 2016 shook public confidence in this fundamental service. Some 5,500 of the town’s 14,000 residents were estimated to have become ill with campylobacteriosis. Some 45 were subsequently hospitalised. It is possible that the outbreak contributed to three deaths, and an unknown number of residents continue to suffer health complications.

The Environmental Health Intelligence NZ factsheet goes on to say the large decrease in the campylobacteriosis rate from 2008 onward has been attributed to the introduction of food safety regulations for poultry production in 2007 and 2008. 

Consequently, the decline represents a drop in the number of food-related cases. It is unlikely to represent a change in the pattern of cases contracted through contact with contaminated water.

Cryptosporidiosis and giardiasis notification rates, 2001–2020      

In 2020, the age-standardised notification rate for cryptosporidiosis was 17.3 per 100,000 people (728 notifications).

The notification rate for this disease has been fairly volatile compared to the other two reported here. As a result, the rate in 2020 is roughly half that of just two years previously – 37.6 notifications per 100,000 people in 2018, the highest rate in the last 20 years of data (Figure 2).

There was a notable drop in the rate of giardiasis between 2019 and 2020 after a period of no real change. The age-standardised rate fell from 34.3 to 22.5 per 100,000 people, which is the largest year-to-year difference on record.

The number of cases underpinning the rate fell from 1,570 to 1,080. The magnitude of the change suggests it may be partly due to reductions in access to healthcare (and cases going unreported as a result) during periods of elevated COVID-19 restrictions during the year.

Drilling into those numbers, we find 5226 cases of campylobacteriosis, 728 cases of  cryptosporidiosis and 1080 cases of giardiasis.

The grand total: 7034.

Fair to say, more figures  comes into considerations in a section headed Waterborne disease notification rates related to drinking untreated water.

In 2019, there were 537 notifications of campylobacteriosis, 211 notifications of giardiasis, and 140 notifications of cryptosporidiosis that reported drinking untreated water during the incubation period. 

But risk factor information was only collected for a proportion of notifications, so these numbers may be an underestimate. 

Risk factor information was collected for only 30.6% of campylobacteriosis notifications, 41.9% of giardiasis notifications, and 41.6% of cryptosporidiosis notifications. 

Risk factor completion rates varied substantially by District Health Board.  

Nanaia Mahuta nevertheless must explain the substantial difference between the figures in the Environmental Health Intelligence NZ factsheet and the 34,000 figure which she has been using. 

She is not alone in using a much bigger figure.

According to the aforementioned TV One report:

A group of scientists are saying the intense political debate surrounding the Three Waters legislation has “drowned out” discussions about the urgent need for safe drinking water.

A Dr Tim Chambers told Breakfast discussions surrounding the bill should be primarily focused on its benefits to public health over anything else.

“The current water system for the Three Waters is not sufficient to protect public health, we know that every year over 30,000 people get sick from their drinking water, and about half a million people have to boil their water to kill bacterial contamination,” Chambers said.

“The point of our article was to highlight that we do have these central public health problems with the current system.”      

The Environmental Health Intelligence NZ website has some data on the quality of our drinking water, too.

It says about 4.1 million New Zealanders (81.4% of the population) were served water from registered drinking water supplies during the 2019–2020 reporting period. The remainder of the population received drinking water from very small community supplies and self-supplies, e.g. rainwater tanks.

Of the population on registered supplies, 95.2% (3.9 million) were served with bacteriological-compliant drinking-water, 80% (3.3 million) with protozoal-compliant drinking water, and 99.1% with chemically compliant drinking water (4.1 million). About 79% (3.2 million) received drinking water that met all three requirements (Table 1).

Table 1: Population on registered community drinking water supplies that had access to safe drinking water, 2019–2020

Access to safe drinking water	Estimated population	Percent
Bacteriological compliance	3,924,540	95.2
Protozoal compliance	3,311,419	80.0
Chemical compliance	4,094,610	99.1
Overall compliance	3,246,369	78.6

Source: Ministry of Health [1]

The factsheet says chemical and bacteriological compliance has remained at or above 95% from the 2010–2011 reporting period onwards.

Protozoal compliance was highest (83%) in 2016–2017, before dropping to its lowest (75%) in 2017­–2018 due to several large supplies losing ‘secure bore water’ status.

Overall compliance in 2019–2020 improved from the previous reporting period, although it remained lower than its peak (81%) in 2016­–2017.