In 1913, Los Angeles' legendary chief engineer William Mulholland watched water flow from the L.A. Aqueduct for the first time and proclaimed, "There it is. Take it." The project drew water from the eastern side of the Sierra Nevada, more than 200 miles away across deserts and mountains, drying up the Owens River and the once-vast Owens Lake, and dangerously lowering eerily beautiful Mono Lake. Over time, it also made modern Los Angeles possible in all its awful glory: sprawling suburbs linked by clogged freeways underneath a blanket of smog.

Later, L.A. tore out its rail system to make room for a booming car culture. And even today, despite the dramatic natural setting – 10,000-foot mountains, 30 miles of Pacific beaches and one of the nation's largest urban parks smack-dab in its middle – many of  L.A.'s 4 million residents have no easy access to nature, making the city one of our most park-poor.

And yet, last year, as the city celebrated the centennial of its original sin – that Owens Valley water grab – it also marked a turning point in its history. Under cover of one of the worst environmental reputations on the planet, Los Angeles is becoming an unlikely model of sustainability.

This coincides with a political transition. In 2013, L.A. elected Mayor Eric Garcetti, 42, who as a city council member was a strong advocate for localizing water sources, cutting energy use, promoting efficiency, confronting climate change, and providing access to parks and nature. His first official mayoral portrait, taken in a kayak on the Los Angeles River last summer, will greet visitors at LAX. That the L.A. River – a trash-strewn, concrete-lined channel famous as a backdrop for murders and movie car chases – has become an official symbol of Los Angeles says a lot about the city's transformation. The river, like its city, is slowly but surely being rehabilitated.

Los Angeles has a solid foundation for this effort. Its 329 days of sunshine a year and ocean breezes give it an advantage, making heating and cooling more energy-efficient. The sprawling city is also, paradoxically, already the nation's densest, with more people on average living in every square block than even New York, thanks to the number of duplexes and apartments in what you might call the suburbs. And it has not one downtown, but many – 88 cities altogether in Los Angeles County, a sort of new urbanist's dream.

Meanwhile, California's overwhelmingly Democratic political landscape is famously friendly to environmental initiatives. The state has moved well beyond debates about whether climate change is happening to begin implementing the country's most progressive policies. Locally, decades of grassroots advocacy to restore the L.A. River – initiated by poet Lewis MacAdams – have been embraced by the political mainstream. The city is also home to RePower L.A., a coalition of environmentalists, labor unions and economic justice activists that works with the city-owned Los Angeles Department of Water and Power to train workers to retrofit homes at no cost to homeowners.

L.A.'s bid to become a 21st century sustainable city starts where its environmental sins began, with water. Despite their hot, dry climate, Angelenos use less water than residents of any other American city with more than a million people, according to the Water and Power Department. Aggressive conservation measures during droughts have led to savings in wet times, too: The metropolitan area currently uses the same amount of water that it did in 1970, even though several million more people live here. Still, L.A. imports approximately 89 percent of its water from hundreds of miles away – the Owens Valley, the Sacramento-San Joaquin Delta and the Colorado River. But the Los Angeles Department of Water and Power has been forced to leave more water in Owens Valley, raising the level of Mono Lake, returning water to the Owens River, and keeping down dust at dry Owens Lake. With other imported supplies likely to be pinched by climate change and increasing environmental demands, the municipal utility is working to capture more stormwater and store it in depleted groundwater basins, clean up contaminated groundwater, and recycle and reuse wastewater.