Residents were warned not to consume any ice, water, beverages or formula prepared with tap water.
Golden State Water Co., which is investigating the source of the contamination, began flushing out water in the system that may contain contaminants, according to a company press release.
Perchlorate is an inorganic chemical used in solid rocket propellant, fireworks, explosives, flares, matches and a variety of industries.
Residents were told not to boil the water, as that process does not reduce the chemical level. Boiling water can actually increase the concentration of the chemical in the water by reducing the H2O content.
Perchlorate interferes with the human thyroid gland, affecting hormones as well as prenatal growth during pregnancies.
Water bottles were available free to the public at Barstow College, 2700 Barstow Rd., according to Golden State Water Co. A water-distribution list was expected to be posted by the company Friday night or Saturday morning.
Water is usually tainted by perchlorate from industrial or aerospace facilities.
Water can be used for purposes other than ingestion, according to a Golden State Water press release.
Water is being distributed 24 hours a day at Barstow College at 2700 Barstow Rd.