Rashi on Isaiah
Your silver has become dross They would make copper coins and plate them with silver, in order to cheat with them.
Ibn Ezra on Isaiah
Thy silver. Metaphor for judges and princes ; this verse is, therefore, followed by, Thy princes are rebellious. Thy silver is become dross. The best of the people are like dross.
Rashi on Isaiah
your wine is diluted with water Your drinks are mixed with water, as is stated in Pesikta (122b). [The word] means ‘mixed,’ although there is no similar word in Scripture to prove it, but the Midrash Aggadah explains (Ecc. 2:2): “Of laughter I said, it makes one mad (מְהוֹלָל)” to mean that it is confused, or mixed up.