David would have sat in ashes as an act of mourning, therefore ashes would have fallen on his food. AT: "I eat ashes like I eat bread" or "As I mourn, ashes fall on the bread that I eat" (See: [[rc://en/ta/man/translate/figs-simile]])
David did not purposefully mix his drink with tears; rather his tear would have fallen into his cup while he mourned and wept. AT: "my tears fall into the cup that I drink" (See: [[rc://en/ta/man/translate/figs-explicit]])