Filthy water cannot be washed.

The proverb uses a practical image—trying to clean with dirty water—to express a moral and logical point: corrupt means cannot produce a clean result. If the tool, medium, or agent of purification is itself contaminated, the act of washing becomes futile or even worsens the stain. Applied to human affairs, it cautions against expecting reform from compromised institutions, seeking justice through unjust methods, or relying on untrustworthy people to restore trust. It also implies that some problems require a change of source—fresh water, a new approach, or a different moral foundation—rather than repeated effort within the same tainted conditions.