In 2007, the State of California —accounting for perchlorate exposure from water, farm products and cow’s milk — enacted a Maximum Contaminant Level (MCL) for perchlorate in drinking water of 6 ppb. This is an exceptionally conservative approach considering studies show perchlorate begins to affect the thyroid at approximately 245 ppb, and below this level there is no measurable effect. No studies show environmental levels of perchlorate cause harm to human health.