The City of Cambridge will soon have to flush money down the drain in order to maintain its storm water management system.

While presenting Cambridge’s new master plan for storm water management to council, city director of engineering Kealy Dedman said the city will need to find $48 million over the next 20 years in order to maintain the existing storm sewer system.

“The plan provides a framework for future work,” said Dedman on Monday.

The shortfall in funding for storm water management is part of the city’s $135-million infrastructure deficit forecast over the next 10 years.

The city is spending $140,000 this year alone to clean catch basins on  Cambridge streets, but funding is only enough to clean half of the 5,050 basins.

The new master plan calls for the city to spend $16.5 million to address the sewer system’s most critical needs. Another $16.6 million is needed to address medium priority work, and $1.9 million to fix low priority issues over the next 20 years.

Dedman explained that on some of the city’s older streets there is flooding during major storms because  sewer pipes are undersized to carry the water.

The new master plan is the first step in a process that will evaluate how best to come up with the funding required to maintain the system. In recent years, both Kitchener and Waterloo have gone to user fees to cover the cost.

“We have a number of options we want to look at,” Dedman said. “We could add it to the tax base. We could come up with a storm water rate like Kitchener or we could come up with a hybrid.”

Those studies are expected to take another year to complete, but the master plan calls for a phased implementation by 2015.