Residents in parts of Houston are being advised to boil their water as Tropical Storm Harvey batters the city and its surrounding areas.

Utility District 6 in Harris County, which covers parts of western Houston, issued the advisory on Tuesday, according to local station Fox26.

“To ensure destruction of all harmful bacteria and other microbes, water for drinking, cooking, and ice making should be boiled and cooled prior to use for drinking water or human consumption purposes,” the notice reads, as reported by the affiliate.

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The Lake Forest Utility is also under a boil water advisory, as is neighboring Montgomery County’s Woodbranch Village.

It is unclear how many residents are affected by the advisory.

The Houston Chronicle on Tuesday reported that Harvey’s death toll has reached 15. The storm first made landfall Friday as a category 4 hurricane.