Building advocates are claiming a modest victory after water regulators approved changes to proposed storm water rules that would give developers a more affordable tool to help manage runoff.

The Los Angeles Regional Water Quality Control Board labored late into the evening July 8 to work out changes to rules that will affect how all buildings, public or private, handle storm-water runoff. The rules ask developers to retain nearly all storm water on-site, a requirement builders said would be costly.

Building industry advocates asked the board to allow biofiltration — the practice of filtering storm water through landscaping and soils before letting it hit drains — as an alternative to retaining water on site in huge cisterns. The board agreed to let builders use biofiltration under some circumstances if the practice removes as many pollutants overall as retaining the water, said Holly Schroeder, executive director of the Building Industry Association for Greater Los Angeles/Ventura.

“We were very encouraged that the board understood that there was no basis for restricting the available best management practices … and that it was necessary to include biofiltration as an option on-site,” Schroeder said.

Before the hearing, environmental advocates had expressed concerns about biofiltration. The water could still contain pollutants, and it could pick up chemicals from other sites as it makes its way to the ocean through drainage systems, they had argued.

“At minimum, you need some sort of performance standard of how that biofilter is working,” Kirsten James, water quality director for Santa Monica’s Heal the Bay, told the Business Times before the hearing. “Our concern with biofiltration is that you don’t get the performance you would using other measures.”

The new storm water permit is more flexible for developers than an earlier version approved by the board last year. State water regulators ordered the board to revisit it after building advocates objected to the way the regulations were drafted and approved.

Water board officials still must work out some of the technical details in the new regulations. The new permit is scheduled to go into effect late this year or early next year.