If I understand the article, combined with my paltry understanding of the law, the argument is the shower should be treated as a point source, which is covered

If I understand the article, combined with my paltry understanding of the law, the argument is the shower should be treated as a point source, which is covered under certain existing legislation. Bathing is not a point source, so is covered by different legislation. Point-sources can have higher concentrations in a small area, like the sand near the showers. These need to be addressed even if the non-point sources are also an issue.