כספך היה לסיגים
Your silver has become dross
Note: the verb hayah with le signifies “become.”
סבאך מהול במים
Your beer diluted with water.
Note: the noun sovei is a kind of drink, some say wine, but Holladay says “suggestion: beer.”
Jerusalem doesn’t need dross in its silver and neither does it need its beer diluted with water. So there you have it!