We found after testing more than 1,000 bottles that about one fourth of the Bottled Water brands (23 of 103 waters, or 22 percent) were contaminated at levels violating strict enforceable state (California) limits for the state in which they were purchased, in at least one sample. We also found that almost one fifth of the waters we tested (18 of 103, or 17 percent) exceeded unenforceable sanitary guidelines for microbiological purity (heterotrophic-plate-count [HPC] bacteria guidelines, adopted in some states, the European Union (EU), and recommended by the Bottled Water industry) in at least one test. While HPC bacteria may be harmless themselves, they may mask the presence of pathogens; some states, the EU and the Bottled Water industry have adopted HPC guidelines to help ensure sanitary source water, processing, and bottling practices. In all, at least one sample of one third of the waters we tested (34 of 103, or 33 percent) exceeded a state enforceable standard for bacterial or chemical contamination, a nonenforceable microbiological-purity (HPC) guideline, or both.