To remove calcium deposits from a glass vase, coffeepot or teapot, scrub with the flesh of a lemon. It's fine to use a lemon wedge that has already been squeezed or that has floated in a glass or pitcher of water. You can sprinkle on a little baking soda or salt to help rub away really stubborn stains.
To scrub away calcium deposits from the inside of a narrow-necked vase, combine a little white vinegar and uncooked rice in the vase and swish them around vigorously. Then pour them out and wash the vase as usual. Your flowers will light up the room even more without those ugly rings on the vase dulling their shine.