Something in the water: part two

Are we taking our water for granted? (12 minute read)

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I can hear the rain falling again. The sound is like a whisper, rising and falling as the rain intensifies then wanes. I turn my head and see raindrops on the window. A wet cat comes inside and jumps onto my desk.

It seems as if it has hardly stopped raining in months. I know that isn’t true, because it’s almost two weeks since I had to wear my wet-weather gear when walking my dog. Nonetheless, we have had a lot of rain in Wellington over the last six months, and we have been much luckier than the rest of the North Island. The catastrophic flooding is still on my mind.

When so much rain falls from the sky, I find it hard to feel grateful for our water. But I should. Every time I turn on the tap, clean and safe water pours out. Billions of people cannot say the same. Two billion lack access to safe drinking water and more than half of those don’t even have a basic supply – a protected source, like a well or a covered spring, less than 30 minutes away. In 2019, more than 1.2 million people died because of unsafe water. Most were under five years old, and in either Africa or south Asia.

The Earth has a lot of water, but most of it – more than 96% – is in the ocean. Of the tiny proportion which is fresh, just over 60% is locked up in the Antarctic ice sheet. Most of the remainder is not, as you might expect, in lakes and rivers, but under the ground[1].

However, water is not static. The water in the ocean doesn’t necessarily stay in the ocean and the water under the ground doesn’t necessarily stay under the ground (nor does the water in the Antarctic ice sheet necessarily stay in the ice sheet, but I’ve written about that already). Water evaporates from the oceans, leaving the salt behind, becomes clouds, falls as rain and snow, filters through the soil, flows through streams, rivers, lakes and aquifers, and eventually ends up in the ocean again. The whole process is known as the water cycle, and it sustains all life on land as well in as lakes and rivers.

When rain and snow fall, though, they seldom land on bare earth. Most land is covered by a blanket of plants, which has a crucial role in the water cycle. If you’ve ever walked in the forest during heavy rain, you’ll understand what I mean. The Earth’s blanket of plants intercepts the rain. It slows down the rate at which the water lands on the soil. Some of it is sucked up from the soil by the plants, and then evaporates from their leaves.

The types of plants present depend on two main factors – rainfall and temperature. If it’s warm and there’s lots of rain, there will be tropical rainforest. If it’s still wet but cooler, there will be temperate rainforest. Areas of the tropics which are somewhat drier have savanna, which has both trees and grass. Milder temperate areas with similar levels of rainfall have deciduous forest, colder temperate areas have evergreen conifer forest.

As a rule, drier and colder areas have fewer trees and wetter areas have more. The wetter a country is, the denser the forest cover. New Zealand, among the wettest temperate countries in the world, was almost completely covered by forest before the arrival of people. The only areas without forest were high up in the mountains, where it was too cold, and some inland parts of the South Island, which were too dry.

By the time Europeans arrived, Māori had cleared the eastern side of the South Island and around a third of the North Island. However, much of New Zealand was still covered with dense forest. That didn’t last. Native forests were logged for timber and converted to pasture, and by 2005 only 25% of New Zealand was covered with native forest.

Why have I wandered into a discussion about the clearance of New Zealand’s forests? Because, in a wet land like New Zealand, the clearance of forests has a dramatic impact on the water cycle and water quality. There is a direct link between what is growing on the land and the quality of the water that flows from it.

image credit: Melanie Newfield

Once New Zealand’s hills were cleared of forest, there was nothing to slow the rain. Grass, especially if it’s grazed, provides nothing like the protection to the land that forest does. Our abundant rainfall began to wash soil into our waterways. Sparkling clear streams turned into turbid torrents. While some sediment in water is natural, especially during heavy rains, land under pasture produces much more sediment than forested land – two to five times as much. Excess sediment in the water changes the character of a river or stream. It blocks the light that plants need to grow, scours the algae from rocks and damages delicate native species like īnanga (one of the species of whitebait). It fills in the spaces between stones where many insects live – insects which provide food for fish.

But sediment isn’t just a problem for the species which live in rivers and streams. It changes the way that rivers flow, filling in channels and increasing the risk of floods. Sediment washes into estuaries, smothering beds of shellfish and fish habitat. Sediment in harbours makes navigation channels shallower and a risk to shipping. Areas which were once sandy change to mud, and support a less diverse range of marine creatures.

But the problem isn’t only caused by farmland. Every time there is a heavy rainfall in Wellington, I see a brown plume of sediment where a stream unnamed on the map pours into the harbour. The catchment area for that stream doesn’t include any farmland – it’s mostly urban. Urban areas also contribute large amounts of sediment to our waterways.

Over the last six months, I’ve seen that sediment plume many times, and I haven’t really given it much thought. But now, I can see it is a symptom of a much bigger problem.

There is much more to look at when it comes to forest clearance and erosion, so I’ve arranged an interview with a scientist who studies erosion. I’ll return to this important topic soon, but now, back to the state of our water.

If sediment was the only type of pollution facing our waterways, it would be quite enough, but it isn’t. There are two other types of pollution which are prevalent in New Zealand. One is disease-causing microbes, which enter the water as a result of contamination by human and animal waste (I’m being polite, but you know what I mean). The other is nutrient pollution – nitrates and phosphates which come from animal waste and fertiliser.

When Europeans arrived in New Zealand, rivers and lakes were clean. Māori had strict rules governing the classification and use of water. Human waste was kept away from waterways and human activity, and used water was disposed of on land, not tipped back into a stream. But there was a rapid deterioration following European settlement. During the 1800s, there were regular epidemics of typhoid, a disease which is common where water is polluted by human waste. There were outbreaks of other waterborne diseases too. Rivers and streams which had been described as “crystal clear” when Europeans arrived, like the Avon/ Ōtakaro in Christchurch, were foul.

We’ve made a lot of progress in the treatment of sewage since then, but microbes associated with human and animal waste are still found in our waterways. We know this because there is monitoring for a type of bacteria usually known as E. coli. Most forms of E. coli are harmless and occur naturally in the intestines of humans and other warm-blooded animals. But E. coli is also abundant in human and animal waste, and can survive in water for four to six weeks. So, if you test water and find E. coli, you know that the water has been recently contaminated, and other microbes associated with waste are also likely to be present. These days, it’s unlikely to be typhoid – the three main culprits are the Campylobacter bacteria, Giardia parasite, and Cryptosporidium parasite.

Rivers and lakes around New Zealand are regularly tested for E. coli, and the news isn’t good. Different sources of data report the result in different ways, but around a third of monitored waterways have high levels of E. coli (one source puts it a bit lower, at 28%, one a bit higher). This doesn’t mean that a third of rivers and lakes are contaminated, because the sample sites were biased towards more populated areas or farmland, rather than remote forest areas. But on the other hand, this is just the waterways with high levels. Another third of waterways had lower levels of E. coli but were still contaminated.

E. coli ends up in our waterways in a number of different ways. Treated wastewater still contains a lot of E. coli, and nearly half of municipal wastewater is discharged into rivers. Farms, particularly cattle farms, also contribute. Cows have a particular habit of pooing over water, so if they have access to streams, then untreated cow manure ends up in waterways.

But E. coli contamination isn’t just an issue with surface water. It can also travel through the soil and into groundwater. Data from 2021 indicate that around half of monitored groundwater sites had detectable E. coli at some point in the previous five years. As with the rivers and lakes, the sample was biased to the kinds of places more likely to be contaminated, but it is still a worrying figure.

The third problem with our waterways is nutrient pollution. I’ve written about this before, when I wrote about nitrate and phosphate fertilisers, but fertilisers aren’t the only culprit. Animal waste, particularly urine, is the main source of nitrates which end up in our water. More than half of that comes from dairy cows. Nitrates are highly soluble in water, and so are washed into waterways and groundwater by the rain. Phosphates, on the other hand, are not very soluble. The main way that phosphates get into water is through the erosion of fertilised soil into waterways. Therefore, if there are sedimentation problems, there are often phosphate problems too. Of course, it isn’t just animal waste which is high in nutrients – human waste is as well. Although sewage treatment removes some nutrients, treated water coming from wastewater facilities is part of the problem. But there are only five million people in New Zealand, and more than ten million cows – and a cow excretes a lot more than a human.

In a natural environment, the amount of nitrogen and phosphorus limits the productivity of the environment. The more nitrogen and phosphorus present, in forms that plants can use like nitrate and phosphate, the more productive the environment. When we are trying to grow a crop, more productivity is generally better, but the same doesn’t necessarily apply in natural environments. Changing the fertility can completely change the balance of species. In waterways, the problems can be particularly acute. I covered one impact of excess nutrients in water two weeks ago when I wrote about toxic cyanobacteria. While cyanobacteria are naturally present in water, excess nutrients cause them to get out of control. Water weeds can also grow out of control. Huge growths of cyanobacteria, algae and aquatic plants suck the oxygen from the water as they decay, killing fish and other aquatic species.

It gets worse. In waterways which have a combination of warm temperatures, low oxygen and lots of decaying material, the type of bacteria which causes botulism germinates and grows. Water birds like ducks pick up the bacteria, and are killed. This year, an outbreak in the Whangamarino wetland in the Waikato killed thousands of birds. Another outbreak killed dozens of birds in Lake Horowhenua/ Punahau near Levin. It’s hard to imagine that this lake was once a major source of food for the local iwi, Muaūpoko – now, it’s one of the most polluted in New Zealand, not only because of waste from people and cows, but also fertiliser runoff from market gardens.

There are other impacts of nutrient pollution too, not least when those nutrients pour into the sea, but I’ll tell you about that some other time. However, before I leave nutrient pollution there’s one more point that I can’t ignore – the impact on human health.

It’s extremely difficult to link environmental pollutants with human disease, after all, it is completely unethical to feed pollutants to people and see if they get sick. Nonetheless, nitrates have been linked with some medical conditions. Very high levels of nitrate in drinking water can cause a disease in babies who are bottle fed. Around 5% of monitored groundwater in New Zealand had enough nitrate to be dangerous to a baby. Other health impacts of nitrates in water are still being debated, but there is some evidence that nitrates are harmful at levels found at around half of monitored sites in New Zealand. The main concern is a potential link to colo-rectal cancer. A recent study in New Zealand estimated that around 100 cases of colo-rectal cancer per year could be linked to drinking water. This is less than the number of cases linked to other risk factors such as alcohol consumption or physical inactivity, nonetheless, it’s reasonable to be concerned about nitrates.

As yet more rain falls on Wellington, I wonder what all this says about New Zealand’s water. What I have read about sediment, microbes and nutrients sounds bad, but these problems must affect every country. How does New Zealand stand up internationally? At first glance, things look good. New Zealand is one of few countries globally where every person has access to water designated as “safe”. Look more closely, however, and the news isn’t so positive. Although we have plenty of water available, back in 2007, we had the second highest consumption of water per capita, after the USA. We are wasteful with our water. In terms of our quality of drinking water and sanitation, we rank some distance behind countries with much more limited resources, such as Israel, Greece, Australia and the USA. When we consider the abundance of water we have, and our very recent history of human occupation, that suggests a serious problem. It seems as if we might be taking this precious asset for granted.

I grew up in suburban Auckland, but I have such happy memories of childhood holidays on a dairy farm that I really don’t want to blame cows. It’s clear, though, that they are a big part of our problem, even if we can’t blame them for everything. So, now I want to understand what it will take to get our water into a better state. Can we keep farming cattle and fix our water? And what impact does pine forestry have? Does planting pine make our water better, or worse? These are questions I will attempt to answer over the next few weeks.

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[1] I didn’t know this until recently, when I read an article by hydrogeologist Steve Shikaze. To learn more about water, it’s worth subscribing to his newsletter.

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