Utility groups are holding off on criticizing the EPA’s new standards for the chemical perchlorate in drinking water, but they are also stopping short of embracing them.

Until the Environmental Protection Agency releases its supporting documents, there is still much that is unknown about how it chose a threshold of 56 micrograms of perchlorate per liter of water, the groups said. Perchlorate is a component of munitions and rocket fuel that can cause thyroid problems when ingested in water.

The EPA is expected to release the documents in the coming weeks. Until then, utility groups like the Association of...