The tap water supply had one of the lowest arsenic levels measured. The bottled water brands all touted their natural purity and goodness because of their long time in the earth, a natural filter. The average concentration of the five bottled water brands was 4.2 ppb, or 233 times higher than the human health surface water standard. The observed values were not unexpected. Seattle's water supply is predominantly from surface waters.
Bottled waters are predominantly from groundwaters.
This is especially true in the western states. If you choose to believe EPA's derivation of the arsenic human health surface water quality standards is valid, then you need to know that bottled water imposes a far greater hypothetical health risk than for many other chemicals and routes of exposures that the media, environmental activists, regulators and politicians typically express outrage about and demand actions on. However, none of the observed concentrations in the bottled water, or the tap water exceeded EPA's present drinking water maximum contaminant level of 50 ppb even though they exceed EPA's surface water quality standards. The interesting thing about the different types of standards is how they are applied. Each is intended to protect human health.