By Karen Brooks Jan 15 (Reuters) - West Virginia officials on Wednesday gave more residents the green light to drink tap water after a chemical spill that fouled drinking water for hundreds of thousands of people across the state. Some 51,000 water customers are now cleared to drink or wash with tap water after nearly a week without it, according to a statement by West Virginia American Water. Consumers were instructed to flush their systems before using the water, which had been barred for use except for toilets since the chemical discharge into the Elk River on Thursday. More than 300,000 consumers were affected after as much as 7,500 gallons (28,000 liters) of 4-methylcyclohexane methanol, or crude MCHM, leaked into the river. Officials have said it might be several days before the entire system, with its hundreds of miles (km) of pipe, was safe to use. The crude MCHM chemical, which is used in coal processing, leaked into the river from a tank at a Freedom Industries site about a mile (1.6 km) upriver from an American Water treatment plant, the biggest in the state. Freedom Industries, which makes specialty chemicals for the cement, mining and steel industries, has apologized for the incident. Water tainted by crude MCHM smells faintly of licorice. Contact with the water can cause nausea, vomiting, dizziness, diarrhea, rashes and reddened skin. The tainted water has flowed downstream into the Ohio River, and utility spokesmen in Kentucky and Ohio said they were monitoring water quality to be sure consumers were not affected. The U.S. Chemical Safety Board and the U.S. attorney for the Southern District of West Virginia are investigating the spill. West Virginia American Water is a unit of American Water Works Co Inc.