Perchlorate in water test.
Perchlorate is a chemical found naturally and in manmade products like rocket fuel, fireworks, and some fertilizers, and it can also form from certain water treatment chemicals.
Perchlorate can affect how your thyroid gland works, which is important for metabolism and for brain development in babies and children.​
The EPA has proposed a health‑based goal for perchlorate in drinking water of 0.02 mg/L (20 ppb).
Most city water systems are not expected to have perchlorate above these levels, but if you have a private well or live near areas with rockets, fireworks, or heavy fertilizer use, testing your water can help you decide if treatment is needed.