Preheat the oven to 375 degrees F. Place the beets in a small roasting pan. Add the water to the pan and cover tightly with aluminum foil. Place in the oven and cook until the beets are fork tender, about 1 hour. Remove from the oven and cool for 15 minutes, reserving the liquid. Remove the skins from the beets and slice 1/4 inch thick. Season the beets with salt. In a saucepan, heat the reserved beet juice and vinegar, over medium heat. Sterilize 1 quart-size preserving jar in boiling water and keep hot. Soak the lids in the boiling water and keep hot. Pack the jar tightly with the beets. Pour hot liquid over the beets, adding enough of the liquid to come within 1/2-inch of the top. With a clean, damp towel, wipe the rim and fit with a hot lid. Tightly screw on the metal ring and process in a hot-water bath for 15 minutes. Using tongs, remove the jar, place on a towel and let cool. Test seal. Tighten the ring. Store in a cool dry place. Let age for 2 weeks.