The company which runs Kenley Water Treatment Works says there would be no immediate risk to water supplies if it floods.
Sutton and East Surrey Water has made preparations to re-route supplies from other sources if the plant has to be shut down.
And it has also treated water storage reservoirs in the area which will maintain supplies for several days and will mean there is no loss of supply even if treated water cannot be produced from the site in Godstone Road, Kenley.
Its employees are working 24 hours a day with the emergency services and Croydon Council to pump out the flood water.
There are also sandbags and other defences around key operating buildings and plant to protect them from the flood water.
- Man charged with raping woman in Croydon town centre
- Police sergeant accused of failing to respond to murder 'lied about investigations and tried to silence colleagues'
- Croydon to lose five 'underused' police bases as Met slashes costs
- McDonald's in Thornton Heath introduces table service
- Man to appear in court charged with exposing himself and racially abusing a police officer