The folks drinking the water were the poor ones, Flint is a island of poor, in mid Michigan. The real issue is not that they made a mistake with pumping acidic water into a urban water system, but when they found out, they covered it up and did nothing. Early on a GM plant complained that they water was too corrosive to use in the plant for cleaning parts. They still did nothing. Nobody wanted to admit to a mistake, and never looked into what it would lead too. Children can suffer life long damage from lead exposure.
A lot of people around here drink municipal water. It was a surprise to a lot of folks that a system could be contaminated like that. I grew up drinking water from the Detroit system.
I don’t know if a Britta filter would filter out lead. I would certainly not trust it too.