The residents of Lake Jackson, Texas-home to about 27,000 people, have been urged not to use tap water by the local authority fearing it might be contaminated with a deadly brain-eating microbe.
The fatal amoeba generally infects people when contaminated water enters the body through nose, reports BBC.
Infections are rare in the US, with 34 reported between 2009 and 2018.
Eight Texas communities were told on Friday night not to use their water supply for any reason except to flush toilets. But the warning was lifted on Saturday for everywhere but Lake Jackson.
The Texas Commission on Environmental Quality said residents of Lake Jackson should continue to avoid using tap water "until the water system has been adequately flushed and samples indicate that the water is safe to use".
It said it is not yet known how long this will take.
Naegleria fowleri is found around the world. The Centers for Disease Control and Prevention (CDC) says the majority of infections in the US have been caused by contaminated freshwater in southern states.
The CDC says people cannot get infected by swallowing contaminated water, and it cannot be passed from person to person.
Those infected with Naegleria fowleri have symptoms including fever, nausea and vomiting, as well as a stiff neck and headaches. Most die within a week.
An infection was previously confirmed in the US state of Florida earlier this year. At the time, health officials there urged locals to avoid nasal contact with water from taps and other sources.