My mistake. The gas was floating on the water.
From BP's website:
WHAT DOES WATER IN PETROL LOOK LIKE?
Water does not mix with petrol and readily settles to the bottom to form a distinct layer which may be clear but usually looks rusty or dirty. Its presence can be confirmed by using water finding paste. If the layer at the bottom of a petrol sample does not give a reaction with water finding paste then it is probably not water and a sample should be sent to a laboratory for analysis.
http://www.bp.com/liveassets/bp_inte...er_in_fuel.pdf