Process for obtaining formic acid by thermal separation of a stream comprising formic acid and a tertiary amine (I), in which a liquid stream comprising formic acid, tertiary amine (I) and water is produced by combining tertiary amine (I) and a formic acid source in the presence of water, water and organic decomposition products of the tertiary amine (I) are removed and formic acid is removed by distillation from the resulting liquid stream in a distillation apparatus, wherein the stream comprising water and organic decomposition products of the tertiary amine (I) which have been separated off is separated into two liquid phases, the upper liquid phase is removed and the lower, water-comprising liquid phase is recirculated to the formic acid source.