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After years of living in the core of this metropolis I moved to the lakeshore, and only then did I begin to properly understand Toronto as a water city. From the balcony of my sixth-floor apartment I can observe thousands of cubic kilometers of shore and water and sky. Standing here, I become an accidental hydrologist in my own small research station. On sunny days, when the water is brushed by wind and cloud, the lake peacocks bright cobalts and ceruleans, streaked with slate and deep azure. There are days when masses of cumulonimbus conquer the city from the southwest, drenching my world as they pass. Then there are the silent days when the clouds enclose my balcony in a soft wadding of mizzled French gray. And on very rare days, when the first bitter winter winds hit the warm lake water, hundreds of vapor plumes shoot up high above the surface.

For an hour or two, the border country between lake and cloud is feathered and unstable. Then the sky clears and the horizon returns once again—the hard wet edge of the planet’s curving rim. The scale of what I can see gives me the measure of what I cannot: the invisible depths, the topography of the lakebed, and the wet shadow of groundwater below that. Invisible as well are the ancient aquifers running beneath the city. They are fed by rain, by snowmelt, by underground reserves—all gradually filtered through the layers of clay, sand, gravel, and rock that make up the ground here.

But this great cycle of water’s transformations is interrupted by the city’s hard skin, an impermeable membrane of roofs and roads, parking lots and laneways, tennis courts and playgrounds. Rain streams off this city-skin: channeled, controlled, eventually swept along storm sewers and into my lake, bringing a plague of evils as it rushes along. “A lake is a sump,” says Julian Caldecott in his survey ‘Water’; everything in its drainage basin flows in one direction, much of it sinking to the lakebed in a permanent, toxic sediment. Caldecott describes some of the contents of this urban wash: “agricultural chemicals, sewage, the oily effluent of car washes, the soapy traces of household detergent, and the accumulated trash of street litter.”

All cities foul their water. In ‘Invisible Cities’, Italo Calvino demonstrates this fate through his imaginary city of Armilla which is nothing but its plumbing: “It has no walls, no ceilings, no floors: it has nothing that makes it seem a city, except the water pipes that rise vertically where the houses should be and spread out horizontally where the floors should be: a forest of pipes that end in taps, showers, spouts, overflows.” Our urban water systems were built to prevent cholera and other water-borne scourges, but their unintended legacy has been the long-term degradation of our cities’ water ecology. The planet now has Armillas clamped to every corner of its surface. It will take a century and more to rescind their dirty works.

This story could have been different. The then-young Los Angeles, for example, could have followed Frederick Law Olmsted and Harlan Bartholemew’s nineteenth-century plan for a green and hydrodynamically balanced city, setting aside large tracts of land for public amenities including “greatly elongated parks several thousand feet in width” running along natural floodways. Their plan would have delivered a radically different LA from the water-starved, privatized city it is today. But the public interest was no match for the interests supporting unfettered private property rights, and the latter won, decisively. LA’s waterways were buried under expensive and disaster-prone real estate.

LA will not be unmade; the development of urban form cannot go in reverse. But we can leverage the progress water policy has made in recent decades and a multitude of promising technologies to design new water cities, cities whose water commons, as they leave the man-made systems, are cleaner than they were when they entered. Achieving this result will require an assemblage of approaches, from local water-storage projects in developing countries to protective greenbelts of undeveloped land wrapping urban centers. We’ll have to plant toxin-absorbing vegetation to break down salt and oil, and pave our roads with surfaces that filter water instead of repelling it. The standard rooftop will be a garden, and every house will have a rainwater recycling system. Above all, to build water cities that improve rather than degrade their water supply, we will need a political culture with the imagination to invest in the long-term public interest.

From my balcony, I see only the small eddy Toronto makes in the global water cycle that surrounds us. This powerful and almost invisibly slow process can easily be ignored, as can its steady corruption by our cities. But ignoring it is precisely what will cause my city, and others, to slip, fold, and buckle at the whim of water. In this volume we explore what could happen if we embraced our watery nature, and learned to care for this essential life-sustaining liquid.