Realists know that urban real-estate projects can recoup spending on energy-efficient equipment but can face runaway costs from the measly supply of water. That’s right: while right-wingers spout about the economic threat of greenhouse-gas regulation, many cities are running out of water for new neighborhoods. A recreation site in Brooklyn hints at a new economic approach to this dilemma: it turns rainwater into a usable asset.

The site is Brooklyn Bridge Park, an 85-acre project hugging 1.3 miles of Manhattan-facing waterfront. The park has earned hisses from some advocates for the poor because its maintenance and operations come from fees that private developers pay to build condos on its edge. This reinforces the suspicion, which I consider simplistic, that the park will feel like a de facto retreat for elites. But it also obscures the savvy engineering the park’s landscape designer, Michael Van Valkenburgh Associates, has set in play.

One feature should goose the imagination of anyone in a city with more empty parcels and more pronounced water shortages, like Atlanta or Santa Cruz: on-site water recycling. The landscape collects rain from nearby buildings, runs it through new pipes into what architect Matt Urbanski calls “weirs” of “water gardens” and into an underground cistern that Urbanski says will provide up to 80 percent of the park’s irrigation. Even with the cost of building new pipes under an abutting highway and the uncertainty of stubbing out those pipes for as-yet-unbuilt towers, this seems likely to net out profitably over time.

Regina Meyer, the park’s administrator, points out that her city-and-state-funded development corporation has to pay for water. That makes each gallon it can generate doubly lucrative: the water gardens create an attractive amenity to yuppie parents and the science teachers who serve them, fortify the park’s green cred, and spare the property from the vagaries of the water market.

And Urbanski argues that the approach, which he said other clients had scratched from their budgets to save construction money, would prove more economical because it avoids the installation and upkeep of drainage. “By conducting water over and through the landscape,” he said, the park puts nature to work. “One day all parks will work this way.”

One thing we can count on as the climate changes is more rain. Another is demand for more soothing places. The water gardens at Brooklyn Bridge Park deserve a serious look.