What do Flint, Mich., and Victoria, B.C., have in common? Huge water-quality problems that suddenly are getting some attention.

Victoria, a tourist haven, promises visitors a beautiful harbor and glorious scenery on the west coast of Canada. However, the city recently announced plans to begin treating millions of gallons of raw sewage that discharge daily into the Strait of Juan de Fuca. It may seem strange that Victoria has gotten away with this for so long, but because tourists didn’t complain, treating sewage was not a priority for the city. Flint, of course, is in news for negligently providing polluted and lead-contaminated water to its residents, although its residents and even General Motors complained about it.

People around the world face similar water-pollution problems. North Carolina’s hog and chicken farms discharge water with high amounts of fecal matter. Some 20 million Bangladeshis, about 12 percent of the population, are part of what the Bulletin of the World Health Organization calls “the largest mass poisoning of a population in history.” Authorities have known about the arsenic in the water supply since the 1970s. The Supreme Court of India has cracked down on the National Capital Region of Delhi for failing to control an estimated 634 million gallons of untreated sewage that flow daily into the river Yamuna, the main source of potable water for India’s capital city.

Political science has some insights on why we neglect water pollution. Here are a few reasons:

1) Water pollution is less visible. Of course, water is key to human existence. But one important insight is that water pollution often is not visible and therefore is overlooked. Citizens tend to focus on problems they can see and experience.

Research shows that routine and visible encounters shape how people perceive pollution. And water pollution often is less obvious than air pollution. Wastewater pipes tend to be buried and discharge effluents into large bodies of water. This means citizens are less likely to notice water pollution in routine encounters — only foul smells and strange colors in the water lead to complaints.

Politicians have incentives to listen to constituents or interest groups, but the politics of visibility means that the process can misfire. For example, citizens living near Allegheny Energy’s coal-fired power plants persuaded some state governments to sue the company for discharging noxious yellow fumes. The company responded by installing scrubbers and using water and chemicals to trap the pollutants. So the company resolved the air pollution but created a less visible water discharge problem in the Monongahela River.

2) Water issues often reflect power inequalities. If you are disadvantaged and face pollution problems, you are in jeopardy twice over, as the vast literature on environmental justice makes clear. The Flint contamination problem in part reflects income and racial disparities; city and state-level officials didn’t have the incentives to respond sufficiently to complaints about water quality. This is a visibility issue, too — people may be invisible as well as problems.

3) Governments ignore linkages between industry and safe water. Trade negotiators often fail to pay attention to the relationship between increased trade and access to drinkable water. Yes, trade deals may promote development, but as countries specialize in water-intensive production (e.g., agriculture or certain industrial products), water quality and access can worsen significantly for the local population that is supposed to benefit from development. The mining industry, for example, is notorious for polluting water.

And income inequalities mean that wealthier people can install home filters or use bottled water and may not push the government to spend tax money to fix the water problems. Thus, countries continue to encourage water-intensive exports, although this creates serious health and other problems for large sections of the society.

4) We take water quality for granted. Because water quality is a semi-invisible issue, it is subject to what Pepper Culpepper calls “quiet politics,” with negotiations and politics taking place in opaque venues that are typically outside public scrutiny. Most of the time, water doesn’t seem politically salient — people take it for granted. This exacerbates inequality, because the people who do experience water-quality problems are often themselves politically invisible.

So what makes Flint particularly important is the fact that the quiet politics of water suddenly became loud. There was some impact from celebrity attention, including Flint-based filmmaker Michael Moore. But Flint’s lead-pollution problems, after being ignored, quickly began receiving attention because the media linked the situation to the broader political debate surrounding “Black Lives Matter.” Flint’s water pollution became yet another instance of racial injustice. The ongoing presidential primaries also brought attention, prompting visits by Hillary Clinton and Bernie Sanders to Flint.

Much of the time, Flint-type problems go unnoticed and unsolved. As political scientists know, policymakers won’t automatically devote attention to problems simply because the problems are serious. They are more likely to devote attention when they will be politically rewarded for devoting attention — or punished if they don’t. So this helps explain Victoria’s longtime neglect of its water pollution, followed by a flurry of activity when it became salient. But as long as water problems are invisible, and more likely to affect people who are themselves not visible or politically important to policymakers, problems like those in Flint and Victoria will continue.

Nives Dolsak is professor in the School of Marine and Environmental Affairs at the University of Washington.

Aseem Prakash is professor of political science, the Walker Family Professor and the founding director of the Center for Environmental Politics at the University of Washington.