The exemption would affect people in western Maryland.
Marylanders can likely expect a hike in their annual sewer bills.
The state legislature finished work Monday on a proposal from Gov. Martin O'Malley to double the $30 fee. Members of the House of Delegates voted 89-48 to accept Senate amendments, including a provision that exempts residents who live in places where wastewater is not discharged into the Chesapeake Bay.
The so-called ``flush tax'' is used to fund a bay restoration account.
House Environmental Matters Committee Chairwoman Maggie McIntosh said the exemption, which would affect people in western Maryland and on the Eastern Shore, is expected to reduce revenues by $1.6 million.