But farmed animals are the most likely source. Runoff from farms increases dramatically as stock numbers (particularly dairy) rise and all forms of agriculture intensify.
And while "nutrients" such as nitrogen and phosphorous are commonly talked up as the major problem, there's another factor inherent in runoff to do with stock: bacteria.
Given your average cow defecates about 25kg of cowpats a day, unpalatable as it is, the New Zealand landscape is covered in s**t.
And the runny poo farmed stock emit now thanks to the antibiotics and supplements they're fed means a lot of liquid output, which seeps into the ground and into our water systems.
E.coli and campylobacter are two types of bacteria often present in animal faeces and both can cause severe gastroenteritis and other illnesses. The former is most readily associated with cows, the latter with poultry.
While bacteria may have a short lifespan outside a host body, they can "encyst": go into a larval-like dormant phase, in which state they could exist in, say, an aquifer for years.
Little is known about how most aquifers function: exactly where their sources are, where and how they flow, or how they react to the various pressure changes below ground. In general, our "knowledge" is informed guesswork based on a handful of partial studies.
Similarly little is known about the myriad animal species - an estimated 500 such in Aotearoa - that have evolved to live within aquifers. But we know these stygofauna help clean the water of nutrients and germs.
When water sources are used for town supply or irrigation, aquifers suffer from less water going into them or more being taken out, or both. This impacts the way they behave, and the stygofauna living in them, to their detriment.
In short, intensive use of water and intensive farming of the land is causing our aquifers to become the equivalent of shallow polluted pools, where harmful bacteria literally slip through the cracks.
The Te Mata aquifer water is an estimated 50 years old, but that doesn't mean there aren't faster routes to that flow. Certainly it's highly likely the week's heavy rainfall somehow caused contaminants to get into the bore.
But there should be no doubt the s**t is hitting the aquifer, country-wide. A similar gastro outbreak occurred in Darfield, Canterbury, four years ago; and Havelock's bores tested positive for E.coli three times since 2013.
So just like the "legacy" nitrate build-up now filtering through from post-WW2 fertilisers, expect more of these ill-health events.
As for a fix, it's not acceptable to suffer chlorine in our tapwater, and forever having to boil it off before drinking. That's treating the symptom, not the cause.
Instead, we must adopt sustainable land management practices that limit the amount of effluent coating our paddocks and fouling our water supplies. Because clean drinking water is our sovereign right.
- Bruce Bisset is a freelance writer and poet.
- All opinions expressed here are his and not those of Hawke's Bay Today.
