INDIANAPOLIS (WISH) — The roof of the Nature Conservancy building on East Ohio Street in downtown Indianapolis stands out as a speck of green in a sea of concrete. It’s among fewer than 20 commercial buildings in the city with a living roof and a cistern to collect rainwater.

The roof is covered with plants, the main roof as a light soil, able to support plants tolerant to both drought and excessive rain conditions. On the secondary roof, in the front of the building, the soil is heavier and able to support larger plants.

All of the plants serve the same purpose according to Chip Sutton, director of communication at the Nature Conservancy.

“I mean it has been a lot of rain; it is an unprecedented amount of rain, but as far as this system, it has done exactly what it was designed to do: keep every drop of rain that falls on this 1-acre site. On this site, it does not leave until it filters out naturally,” said Sutton.

Three separate roofs on the building are connected to a series of pipes and drains to carry rainwater from the roof, through a series of pipes to a cistern in the basement.

It takes one inch of rain to fill the 2,500-gallon cistern in the building’s basement. All of the water that falls is captured and stored or used, a process called harvesting. The only water the Nature Conservancy buys is used for drinking water. Rainwater is used to flush the toilets and irrigate the plants.

When construction on this building began 10 years ago, the expectation was to cut water usage by 40% annually from rainwater harvested from the roofs. Today the nonprofit estimates savings are closer to 80% annually.

“That was one of the goals of having this building: to show as many people as possible that this sort of green building is really beneficial from an economic standpoint as well as an environmental standpoint,” said Sutton.