Brent Bierbaum climbs into the ditch running alongside one of his corn fields and dips a nitrate testing strip into the water. He checks the strip: the reading is somewhere between 10 and 20 parts per million. It confirms the water running off this field contains nitrates at levels that would be unsafe, and illegal, in drinking water.

Brent, whose family have been farming in this part of south-west Iowa for five generations, never used to worry about the runoff from his fields. On a hot day, cutting thistles in the corn fields, he’d go down to the creek and drink straight from the tile line – the water coming off the fields. “Cold, clean – it’s the best water around,” he says.

Things changed when his local town, Griswold, started having problems with their drinking water. Nitrates are a soluble form of nitrogen that is added to fields as synthetic fertiliser and animal manure; nitrates from Brent’s fields, and other neighbouring farms, were making their way into the town’s wells. Nitrate from farmland in Iowa is already a major contributor to the chemicals making their way to the Gulf of Mexico via the Mississippi river, suffocating marine life in the “dead zone”. Suddenly what had been a distant problem, more than a thousand miles away, was on the doorstep, threatening the health of friends and neighbours.

“Oh my gosh,” he says. “We all have friends who drink the water in town; we drink the water in town, so we all had an interest in it.”

Like most small towns in rural Iowa, Griswold is surrounded by vast fields of corn and soya bean. Giant grain silos glinting in the spring sunshine are all that punctuate the landscape for miles around.

Iowa’s world-famous soils are packed with nitrogen – a gift from nature that allowed commercial agriculture to take root here – but decades of adding synthetic fertilisers and animal manure to drive production has loaded the land with nutrients it can’t hold on to. Crop production in Iowa is still the main source, but animal manure from the state’s 20 million pigs has contributed to the problem.

Brent Bierbaum tests the water in a ditch alongside one of his family’s fields. Photograph: Anna Jones/The Guardian

The legal limit for nitrates in drinking water in the US is 10 parts per million, equivalent to 10mg per litre. It was introduced in 1962 to guard against blue baby syndrome, a potentially fatal condition affecting newborn babies and infants under one year old. It’s caused by nitrates starving the body of oxygen, literally turning babies blue.

Three public wells, fed by an underground aquifer, provide drinking water for Griswold’s 1,000 residents. Between 2012 and 2019, according to Griswold City Council, a single well recorded 21 incidents over 9mg/l and four incidents over 10mg/l. Another recorded 18 incidents over 9mg/l.

Studies by the National Cancer Institute found that drinking water with an average level of 5mg/l of nitrate, over a long period of time, may increase the risk of certain cancers. Other studies have linked nitrate intake above 5mg/l with birth defects in babies.

Julie Adams, one of Griswold’s busy city councillors, took it upon herself to knock on doors and ring around new mothers and daycare nurseries, warning them of the risks: “I tell them, ‘If you have small babies do not use the tap water when you’re making formula. Use bottled water. Just to be safe.’”

The ‘dead zone’

The problem is that nitrates are on the move, and in higher volumes than ever before. Iowa is 80% farmland and exports more nitrate to the Gulf of Mexico than any other US state. Nitrogen and phosphorous are the chemicals that suffocate marine life in the so-called ‘Dead Zone’.

It’s not an isolated problem. A report from the Environmental Working Group (EWG) revealed that, across the US, 1,700 municipal water utilities – most of them rural – regularly have nitrates above the 5mg/l safe limit. Worryingly, 120 public waterworks breach the 10mg/l legal limit. On top of that, Iowa has up to 290,000 private wells, many on remote farms like Brent’s, which are not required by law to be tested.

The state of Griswold’s wells set alarm bells ringing at Iowa’s Department of Natural Resources, which oversees water quality. They called a meeting and delivered a sobering ultimatum – either bring nitrate levels down or the council would be ordered to spend $1m on a nitrate removal facility. It would wipe out a third of Griswold’s $3m annual budget.

Councillor Julie Adams at her home. Photograph: Anna Jones/The Guardian

“We can’t afford that,” says Adams. “We need a new fire station, we need to knock down a derelict building, we need a new park for the children to play in. We have many more needs than we have money.”

Fellow city council member Ryan Askeland, who owns and runs the town’s only restaurant, was also at the meeting: “They described the harm it could do to infants under one-year-old and I thought, ‘Holy cow, what they’re putting on the fields is poisoning us.’”

Checking himself, he looks around his restaurant and softens his language. “An uneducated person would say ‘poisoning’. What I mean is, it was contaminating the water.”

Griswold is a close-knit community. The town folk value their farmer neighbours and are careful not to cause conflict. “Over 80% of the people in here are from the farming community at any given time,” says Askeland. “Everything in this area is pretty much funded by agriculture. We are all on the same team.”

Iowa is agriculture. The state produces the most of many things – corn, hogs and eggs – and jostles with neighbouring Illinois for the top spot in soya bean production. Hefty property taxes paid by farmers keep the lights on in rural towns, many with dwindling populations, right across the midwest. It’s no surprise there is inexhaustible goodwill towards them – even when some farming practices threaten their drinking water.

In Des Moines, the city’s waterworks did blame the farmers, and brought a lawsuit, but it failed. Des Moines Water Works was bitterly disappointed – particularly their outspoken CEO, the late Bill Stowe, who died from cancer earlier this year. A controversial figure in Iowa, Stowe waged war on “unregulated industrial agriculture” and what he called the “powerful agro-elite”. He likened those who downplay Iowa’s water quality issues to climate change deniers and held the farming industry responsible for the public health risks associated with high nitrates in drinking water. “If a baby died,” he said, “there would be a clear path between agriculture and the death of that baby.”

Speaking to the Guardian shortly before his death, he said: “It’s disheartening: the image of Iowa as a sacrificed state at the mercy of industrial agriculture. We will continue to be advocates for agricultural producers taking responsibility for the water pollution they are inflicting on the rest of us downstream.”

A water quality notice hangs near the beach at Big Creek state park, in Polk City, Iowa. Photograph: Charlie Neibergall/AP

In rural north-west Iowa, Gordon Garrison, a retired corn and soya bean grower, hopes to succeed where Des Moines Water Works failed.

Garrison is allowing his farm to return to wetland. He points down to the creek where he has reintroduced beavers, and beyond to a single-storey white building in the neighbouring field – a hog barn, or confined animal feeding operation (Cafo), housing up to 8,800 pigs.

“That building has no consideration for environmental impact at all,” he says. “I have got algal blooms in my downstream water. After they bought the farm, the nitrate level almost doubled.”

The pig farm is owned and operated by Minnesota-based company New Fashion Pork. They bought 77 hectares (192 acres) next to Garrison’s farm in 2014 and started producing pigs two years later. The building sits over a pit that can hold more than one million gallons of liquified hog manure, and Garrison claims that the manure was spread illegally on snow-covered ground in December 2018.

Iowa Department of Natural Resources (DNR) issued New Fashion Pork with a notice of violation and a fine of $4,800 (£3,900). Garrison filed a citizen’s suit, which he believes will be a precedent-setting case in the US. Garrison’s hope is that his legal action will set a precedent and pave the way for tougher regulation of pig Cafos in the context of water quality protection.

New Fashion Pork, which runs 53 pig confinements across Iowa, has said it complies with all manure application requirements and obtained permission from Iowa DNR to surface apply manure. “Field conditions were not good in most of the state last fall and winter and the DNR routinely granted permission to producers to surface apply manure in December of 2018,” said a legal advisor for New Fashion Pork. The company also said that nitrate loss from crop fields is affected by many factors, but that the source of the nitrogen (manure or commercial fertiliser) has little, if any, effect on the amount of nitrate loss.

“The only way to solve this problem is if there’s peer pressure,” says Gordon. “We can’t let some guys abuse the system and profit from it. If they prevail in this lawsuit that’s just a signal to build more and more.”

An aerial view of the Iowan countryside: crop fields stretch out as far as the eye can see. Photograph: Charles Ommanney/Getty Images

Ditching the manure of 20 million pigs

There are already more than 7,000 hog farms in Iowa raising around 20 million pigs at any one time; that’s a lot of manure for one state to dispose of. It’s long been said Iowa needs a third cash crop to break the dependence on corn and soya bean. As one farmer put it: “We’ve found one. It’s called bacon.”

But it’s not without risk. In Marshall County, 25-year-old Ryan Pickard is a third-generation row crop farmer, growing 1,820 hectares of corn and soya bean who diversified into custom pig production in 2015 to spread the risk from low grain prices.

Ryan and his 29-year-old brother, Brandon, borrowed nearly $1.5m to build two Cafos, with one still under construction. They each house 5,000 newly weaned, 18-day-old pigs. They’re thinned out as they grow bigger, with half being moved to another site. Ryan fattens the remaining 2,500, which are sent for slaughter direct from the farm.

The brothers do not own the pigs and receive none of the profit. They are paid instead for “head space” in the building. They do own the manure, which drops through slats into a pit holding up to 800,000 gallons. They also own all the risk associated with it.

Ryan is ruled by the pit. When it’s full, it’s full – and must be emptied. It’s spread once a year on a nearby 80-hectare (200-acre) corn field. He tries to plan ahead, working around the weather, but if there’s a spill or run-off, the full responsibility rests on him.

“It’s something I think about constantly,” he says. “If not managed properly it could give me a very bad name and I don’t want that. If the pit leaks, we need to find the problem and fix it before we can go back into production.”

For Ryan the threat of being shut down is all the incentive he needs to manage the pit properly. But across Iowa there are more, and ever louder calls, for real regulation to protect water quality.

At the moment there is nothing in place but a voluntary approach, as laid out in Iowa’s much-lauded nutrient reduction strategy (NRS) which calls for farmers to plant 5m hectares of cover crops, which are proven to reduce run off and pollution. Iowa-based environmental and citizen groups believe the NRS is a dismal failure, with no deadlines, no rules and no enforcement. The most generous estimate suggests cover crops have been planted on 307,500 hectares, just 2% of Iowa’s farmland.

Jennifer Terry, executive director of the Iowa Environment Council, says. “It’s unfair to pretend to Iowans that we can get there in a reasonable timeframe via voluntary means. It will take us thousands of years to get these practices in place at the current rate of implementation.”

And do cover crops even work? In Griswold, faced with a $1m bill, the town started working with four local farmers to plant cover crops in the 250-hectare capture zone around the town wells. Brent Bierbaum is one of the farmers involved. “We explained to the farmers what was going on and that we were really hoping they would help us, and they were all on board,” says councillor Julie Adams.

But despite their efforts, water quality has still not improved. Nitrate levels spiked in 2017 and 2018. At the most recent inspection in February, one well showed an increase of nitrates to 10.5 mg/l.

According to the Department of Natural Resources, nitrates may continue to leach because of legacy nitrogen stored in the soil and continued rates of fertiliser application. One study of a row crop field that had been restored to prairie found that groundwater nitrate concentrations reduced at a snail’s pace of approximately 0.6 mg/l per year.

Adams is willing to give it more time but admits the trend is going the wrong way. Fellow councillor Askeland has resigned himself to what’s coming.

“I think cover crops are a band aid,” he says. “We’ve got a wound that’s bleeding and eventually we’re going to need something bigger than a band aid – and that’s the filtration system.”