Q. When I was a child we had raisin wine on Pesach. Is there anything wrong with this?
A. One must drink four cups of wine at the Seder. Grape juice is used by some who cannot take wine. The wine may be diluted with grape juice or, if there is no alternative, with water. Raisin wine is acceptable for a person who cannot drink wine or grape juice.
If necessary, the din also allows “the beverage of the country”, i.e. the kind of drink one serves to a guest (Mishnah B’rurah 472, note 37). This would appear to include tea and coffee, though some forbid them. Drinks that are not kosher for Pesach, e.g. whisky and beer, must not be used. Rabbi Moshe Feinstein rules against using soda water to fulfil the mitzvah, as this is merely used for the sake of thirst (Ig’rot Moshe, Orach Chayyim, vol. 2, no. 75).
According to Sephardi custom, when a drop of water is poured off as each of the Ten Plagues is enumerated, a drop of water is poured out at the same time. This derives from the Kabbalah, which says that when God punishes a people He tempers justice with mercy. The wine stands for punishment; the water which dilutes it represents mercy.