The early signs are that the relief reservoirs may be helping to ease flooding problems in Woldingham and Whyteleafe.
Even though the holding ponds are not fully operational yet, a Tandridge District Council spokeswoman said: "Even during the testing we have noticed they do relieve the pressure on the Bourne downstream at Wapses Lodge.
"Further trials are being carried out this week before they are fully operational.
"Every advantage is being taken of a week of low rainfall this week to manage flows and move as much water as possible through the system so storage capacity can be built up to counter any more intense rainfall events to protect Tandridge and Croydon residents from further property flooding."
Tandridge District Council, Surrey County Council, Croydon Council, the Environment Agency and Thames Water have all been working together on this.
