Jim Graham, Noel Roberts: Ground water never safe

Jim Graham (left) is an Environmental Scientist and Water New Zealand's Principal Advisor Water Quality, while Noel Roberts is Water New Zealand's Technical Manager.

The findings and recommendations of stage 2 of the Havelock North water contamination inquiry released this December jolted many New Zealanders out of their 100 per cent pure misconception about groundwater quality.

The inquiry made it clear that untreated ground water is not safe to drink because it cannot be guaranteed as free from contamination.

While it pointed to widespread systemic failure in our drinking water systems, it also identified problems with our drinking water safety net, the decade-old New Zealand Drinking Water Standards.

Ten years ago these standards were widely regarded as leading edge with new ideas for ensuring drinking water safety. However, since then they have not been updated to keep pace with improvements in our knowledge and drinking water treatment technology.

Havelock North District Council was assessed as being compliant with the Drinking Water Standards despite being found by the inquiry to have failed to embrace a high standard of care.

Under the standards, water can be classified as so-called "secure" bore water and this was the case in Havelock North. That means it can be pumped through to residents' taps without treatment and with very little monitoring for contamination.

In order to be classified as secure bore water, a water source must meet all of four categories:

-It needs to have been underground for at least 12 months, as it is considered that after this amount of time all micro-organisms and viruses have died or been filtered out.
_ Bores need to be at least 30 metres deep, but is some cases can be as shallow as ten metres.
-Bored heads need to be sealed at the surface and constructed in a way that prevents surface water from entering the bore.
-It needs to be shown that E. coli has not been in the water over a long period of time.

A decade after the standards were adopted, the Havelock North inquiry has suggested that there's no such thing as secure bore water.

For instance, it was shown at Havelock North that water which was thought to have been underground for more than 20 years had in fact been mixing with surface water after heavy rain as young as 26 hours and this is likely to have been the cause of contamination of the Havelock North supply.

Part of the problem was that the standards only required checking of aquifer water age every five years. We now know that changes to underground water age can occur much more quickly than that.

We now also know that water can travel way faster in an aquifer than previously thought, up to 200 metres a day has been identified when previously about half a metre a day was considered usual.

The Canterbury and Kaikoura earthquakes have shown us that seismic events can considerably change things underground including water flow paths, rates and levels. This can affect water quality without those changes being evident on the surface.

The reality is that it is hard to know exactly what is happening to water that is below ground.

New information suggests that our thinking and the standards of 10 years ago were flawed and provides a serious wake-up call as to what we had regarded as safe and pure drinking water. It has led the Havelock North Inquiry to call for mandatory treatment of all water supplies unless there are very exceptional circumstances. We strongly support that recommendation. The inquiry has also recommended that the drinking-water standards are updated. We agree. And soon.

It's clear that the time for regarding our underground aquifers as uncontaminated and impenetrable is over. Councils and their communities take a big risk with the health of residents and visitors if they choose to provide untreated groundwater for drinking in the belief that water treatment is either unnecessary or too expensive.

The truth is, as Havelock North residents have unfortunately discovered, it is a lot more traumatic and costly to deal with water supply contamination after the event than it is to prevent water supply contamination in the first place.

Jim Graham is an Environmental Scientist and Water New Zealand's Principal Advisor Water Quality, Noel Roberts is Water New Zealand's Technical Manager. Both sat through the weeks of evidence presented at the Havelock North Drinking Water Inquiry. Views expressed here are the writer's opinion and not the newspaper's. Email: editor@hbtoday.co.nz