From the Wisconsin Department of Health and Family Services chemical fact sheet for Trichloroethylene:

DO STANDARDS EXIST FOR REGULATING TRICHLOROETHYLENE?

Water: The state and federal drinking water standards for TCE are both set at 5 parts per billion. We suggest you stop drinking water containing more than the standard. If levels of TCE are very high in your water (greater than 300 parts per billion), you may also need to avoid washing, bathing, or using the water for other purposes.

Air: No standards exist for the amount of TCE allowed in the air of homes. However, there are workplace limits. We use a formula to convert workplace limits to home limits. Based on the formula, we recommend levels of TCE in air be no higher than 1 part per million (ppm). You can smell TCE when the level reaches 25 ppm. If you can smell the chemical, the level is too high to be safe.

Note: We'll be featuring various state health department fact sheets and regulations for TCE. Wisconsin just happens to be first. If you'd like to recommend others, please contact us.