More than 60 firefighters are at the Kenley water treatment works battling to stop it flooding.
Crews have been there since 9.30pm last Thursday pumping 24,000 litres of water a minute away from the affected waterworks.
Last night eight firefighters were at the site in Godstone Road, along with three high volume pumps.
The London Fire Brigade anticipates remaining on site over the next two days.
Fire commissioner Ron Dobson said: “Firefighters have been working very hard throughout the last few days to pump water away from the facility and protect it from flooding.
“The waterworks supplies tens of thousands of homes in the area so our crews are working extremely hard to bring this incident to a quick and safe conclusion.”
Croydon Council leader Councillor Mike Fisher said: “The council is working closely with emergency services, local water companies, and neighbouring authorities to ensure plans are in place to deal with the situation if it worsens.
“We are doing everything we possibly can to prepare for flooding and to make local residents and businesses, who will be potentially affected aware.
“It is important to emphasise that the majority of Croydon will not be affected but we would ask everyone to be vigilant, keep an eye on what’s happening and take action as required.”
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