The North Texas Municipal Water District's annual chlorine maintenance ends Monday. According to the city, the water may take up to a week to smell less like chlorine. Residents in Frisco and other cities serviced by the water district have raised questions about the safety of chlorine maintenance after environmental activist Erin Brockovich criticized the process on her Facebook page. Frisco Mayor Jeff Cheney and City Manager George Purefoy published a letter to residents Monday to address some of those concerns. The district released the results of an independent lab report last week showing the levels of a potentially toxic byproduct of the ongoing water-treatment process rose this month but remained within the federal regulatory standards.