PEX is not currently banned in California. It was previously banned; however, in 2010, PEX was approved for use by the California Building Standards Commission. This continues to be a topic of debate, with builders and plumbers for using PEX and the pipefitters union and environmentalists against using it.
Initially, PEX was banned because it was reported that there were chemical traces from the PEX pipes seeping into the drinking water. Since then, additional third-party testing has shown that PEX is safe for consumers, even when comparing PEX vs. PVC.