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.
- Private developer takes over plans to build more than 500 home on site of former council HQ
- Thornton Heath teenager caught with terrorist handbook at Stansted Airport on way to fight for Isis in Syria
- Commuter hell: See if you're travelling to work on one of the most overcrowded trains in the country
- Grime star Stormzy takes over Thorpe Park for his birthday
- £10,000 raised to fly home body of Brazilian teenager who drowned while staying with dad in Croydon