épurer

To purify or refine something physically (épurer l'eau, épurer l'air) and, in a historically loaded political sense, to purge an institution of undesired members — épurer l'administration echoes the épuration (purge) of collaborators after WWII, so the word carries real historical weight in political contexts.

• Cette station épure l'eau avant de la rejeter dans la rivière. — This plant purifies the water before releasing it into the river.
• Le réalisateur a épuré le scénario pour ne garder que l'essentiel. — The director trimmed the script down to keep only the essentials.
• Le nouveau régime a épuré l'administration de ses opposants. — The new regime purged the administration of its opponents.

The political "purge" sense is historically loaded in French (linked to l'épuration after the Liberation of France in 1944-45) — learners should be careful using épurer about people or institutions, since it can carry much stronger connotations than the neutral technical sense of purifying water or air.