LAKE JACKSON, Texas (AP) — Texas officials on Saturday lifted a warning for all but one Houston-area community to stop using tap water because it might be tainted with a deadly brain-eating microbe.

The Texas Commission on Environmental Quality warned the Brazosport Water Authority late Friday of the potential contamination of its water supply by naegleria fowleri.

The authority initially warned eight communities not to use tap water for any reason except to flush toilets, but on Saturday it lifted that warning for everywhere but Lake Jackson. The city of more than 27,000 residents is the site of the authority’s water treatment plant. The advisory also was canceled for two state prisons and Dow Chemical’s massive Freeport works.

The advisory will remain in place until the authority’s water system has been thoroughly flushed and tests on water samples show the system’s water is again safe to use. The authority said in a statement that it was unclear how long it would be before the tap water was again safe.

The authority’s water source is the Brazos River.

Naegleria fowleri is a free-living microscopic amoeba, or single-celled living organism commonly found in warm freshwater and soil, according to the U.S Centers for Disease Control and Prevention. It usually infects people when contaminated water enters the body through the nose, from where it travels to the brain and can cause a rare and debilitating disease called primary amebic meningoencephalitis.

The infection is usually fatal and typically occurs when people go swimming or diving in warm freshwater places such as lakes and rivers. In very rare instances, naegleria infections may also occur when contaminated water from other sources (such as inadequately chlorinated swimming pool water or heated and contaminated tap water) enters the nose.

The contamination of U.S. treated public water systems by the microbe is rare but not unheard of. According to the CDC website, the first deaths from naegleria fowleri found in tap water from treated U.S. public drinking water systems occurred in southern Louisiana in 2011 and 2013. The microbe was also found in 2003 in an untreated geothermal well-supplied drinking water system in Arizona, as well as in disinfected public drinking water supplies in Australia in the 1970s and ’80s and in 2008 in Pakistan.