As the drive for accountability in government spending increases, many are looking for ways to keep from paying the full price for programs that don't work.

In Washington, D.C., that desire has led to the first-ever environmental impact bond, issued this fall by DC Water, the city's water and sewer authority. The $25 million bond will pay for new, green infrastructure like rain gardens and permeable pavement to reduce stormwater runoff.

But if the projects don't work as expected, that's where the new financing structure comes in. Under the terms of the bond, which DC Water sold directly to Goldman Sachs Urban Investment Group and the nonprofit Calvert Foundation, the utility stands to get a multimillion discount on its total borrowing costs if the project doesn't meet a certain threshold.

It's essentially an insurance policy on the project's effectiveness. Here's how it works: After five years, the new infrastructure will be evaluated. If stormwater runoff isn't reduced by at least 18.6 percent, investors will owe DC Water a $3.3 million "risk share" payment. The payment represents a near-full refund of the 3.43 percent interest rate payments DC Water made during the first five years of the bond. After that, the bonds would likely be refinanced into 25-year bonds. DC Water would also drop green infrastructure projects and go back to so-called gray ones (like pumps and water tunnels) to reduce runoff.