Near the top of the daily challenges that Flint residents face in a city without safe drinking water is how and where to shower. Families are going to extraordinary lengths to find places where they can bathe without fear, taking measures that many say add to the upheaval that has been part of their lives since state officials confirmed last fall that their water was contaminated with dangerous levels of lead. As of Tuesday, investigators had talked to 538 people who complained of rashes or other skin problems. Of those, 388 qualified for the study because they had an active rash that appeared after the city switched back to Detroit water.