The San Diego Unified School District argues that any amount of lead in school drinking water is damaging to children. At the same time, it has found lead in water at some schools, does not remove all of it and is allowing kids to drink it. The argument that lead is in the water and is hurting kids has become the main selling point for Measure YY, the district’s school bond campaign. Though the bond is expected to generate $3.5 billion, only $45 million – less than 2 percent – would go to remove lead from school district water, district documents show.