Washington D.C.’s water management organization, DC Water, issued a statement Friday warning residents against drinking tap water after a contamination risk threatened the water supply of tens of thousands of residents in downtown D.C. and nearby areas. NBC4 reports that although there is no concrete evidence of contaminated water, an open valve near Howard University reduced the pressure in the system, which could lead to contamination. Residents have been advised to boil all water intended for drinking and cooking, and the advisory is expected to last between 24 and 48 hours. Authorities have not released information on how the valve was opened. “Our teams will continue to test samples of the water, and we will lift the advisory when we determine the water is safe,” the water authority told NBC4.