A contaminated water source does not pose a danger to the public, according to the Environment Agency.
The green watchdog has been monitoring the situation since petrol-type contaminants were found in a groundwater supply.
The pollutants were discovered next to the A27 between Falmer and Lewes in April but the source has yet to be identified.
Newmarket petrol station operated by BP on the A27 was closed after a borehole found ongoing contamination.
A borehole was also drilled beside the Texaco petrol station opposite the BP garage but no contamination was found.
Southern Water has been running tests on its supplies to protect the public.
The contaminated source is situated between two boreholes which supply the area.
But the Environment Agency has said the water company is successfully ensuring the pollutants do not enter the public supply.
Simon Deacon said: "We are working hard to investigate where this contamination has come from and what damage it has caused.
"BP has drilled several boreholes and is continuing to monitor these.
"Only one has identified a continuing trend of contamination in the groundwater. Unfortunately we do not know yet where the contamination has come from."
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