California is proposing a tougher target for the rocket fuel chemical perchlorate in drinking water, citing studies that linked minute amounts of the chemical to impaired thyroid function in infants.

The current health goal – for water considered safe for everyone – is 6 parts perchlorate per billion parts water. On Friday, the state proposed lowering the goal to 1 part per billion.

While not an enforceable limit, a health goal is a step in determining a legal limit for a drinking water contaminant. The current legal limit for perchlorate is 6 parts per billion.

After a public-comment period ends next month, the health goal could be finalized and forwarded to another agency, which could consider adopting a tougher drinking-water standard.

Perchlorate is found in many Inland water sources. Suppliers treat or blend the water to meet the limit before delivering it to consumers.

Among the contaminated Inland sources are the Colorado River and several groundwater basins. The Metropolitan Water District, which serves about 19 million people in Southern California, relies in part on the Colorado River for its supplies. The river now carries about 1.5 parts per billion, MWD spokesman Bob Muir said.