Mormons and the "Lord's Supper" - Bread and Water

Bread and water for the elements in the Lord's Supper? Read the details as presented by the Mormonism Research Center.

A two-paragraph snippet:

Water was not always used in the LDS version of the sacrament. From the beginning, wine was used, after the longstanding Christian tradition. This is seen in the sections of the Doctrine and Covenants regarding the organization of the Church as well as the Word of Wisdom (D&C 20:75; 89:5,6). The use of wine was called into question by Sidney Rigdon, a staunch temperance advocate, who joined the Church in August of 1830. Accordingly, Joseph Smith received a vision of the Lord in the same month in which an angel of the Lord told him that he was not to purchase wine or strong drink of his enemies, and that wine was not necessary to proper observance of the sacrament (D&C 27:1-4). The first time water was used in the sacrament was in 1837, though the issue would vacilate back and forth until 1900. After the turn of the century, water became the permanent element in the LDS observance.

What is so important about the use of wine, juice, or water in the sacrament? For centuries, there has been a difference of opinion whether wine or juice should be used, which controversy continues even today. Why is the use of water such a problem? Isn't the substance used a symbol of something else even more imporant?