מֵימֵ֙ינוּ֙ בְּכֶ֣סֶף שָׁתִ֔ינוּ עֵצֵ֖ינוּ בִּמְחִ֥יר יָבֹֽאוּ׃
Ang aming sariling tubig ay binibili namin ng pilak bago mainom; ang aming kahoy ay dumarating sa amin nang may bayad.
Siftei Chakhamim
Although we have in our possession manna to eat. Rashi mentions “manna to eat” even though the verse only writes about water, because Rashi is answering the question: If he had not spoken the king of Edom about food, what benefit would they have in them purchasing water, since this was of minor benefit to them? Rather, Moshe must have also said that they would purchase food from them. The reason that the verse specifically mentions water was to teach something additional; that they also wished to purchase water from them, even though it was not customary to purchase water. We see that from Yirmeyahu who lamented (Eichah 5:4), “We drank our water for money” (Mahari).