Do you have hard water? That might do it. Also, presumably you're fine with vinegar, but for anyone else who prefers less fragrant cleaners, citric acid (usual

Do you have hard water? That might do it. Also, presumably you're fine with vinegar, but for anyone else who prefers less fragrant cleaners, citric acid (usually available as a powder) can almost always be substituted for vinegar with comparable to better results.