President Barack Obama has accepted West Virginia's request for a disaster declaration, which allows federal aid to be used.
Jeff McIntyre, president of West Virginia American Water, told the Associated Press news agency: "Until we get out and flush the actual system and do more testing, we can't say how long this will last at this time.
Charleston Mayor Danny Jones said at a press conference on Friday the spill had been "devastating to the public at large and to the people that live in our city".
Freedom Industries has said the chemical, 4-methylcyclohexane methanol, could be harmful if swallowed and cause skin and eye irritation.
In a statement, the firm said it was working with local and federal officials and "following all necessary steps to fix the issue".
The West Virginia National Guard planned on Friday to deliver bottled water to emergency services.