Specialist dyes were put into a water system to track where drainage water flows underground and where it comes out in the bid by Newton Mearns residents to stop the development of 44 houses and 14 flats.
The campaigners say they took the action after taking advice from the Scottish Environment Protection Agency (SEPA).
Group spokesman Michael Bradnam said "The results confirmed our concerns of a potential flood risk from a new housing development near Ayr Road at Cheviot Drive.
"Removal of a peat bog behind Cheviot Drive and the construction of roads and houses in the current greenfield site will all increase water run-off.
"The mapping demonstrated the watercourse weaves its way for the first two kilometres through private residential gardens.
"A number of these properties are already subject to flooding."
The campaigners have now produced a video of their results and have released it on the internet.
They hope that their work will convince East Renfrewshire Council to block the plans by developer Stewart Milne Homes.
Mr Bradnam added: "The developer has agreed to meet us to hear our concerns. We see that as a positive step forward."
Jonathan Fair, managing director of Stewart Milne Homes, Central Scotland, said: "We've obtained all the necessary technical and regulatory consents for a detailed and competent drainage solution.
"We are fully aware of the current flood issues on the land at Ayr Road.
"We have designed a drainage network that will control the surface water on the site.
"SEPA have reviewed and assessed our plan and are happy. The council have given approval as Flood Authority and Scottish Water have provided technical approval.
"We have worked closely with each of these organisations to deliver a long-term strategy for the site and we are confident with our approved plan."