When writing vows for a sand wedding ceremony, start with an introduction explaining the purpose of the ceremony. In the next section, either the couple recites statements of commitment to each other or the officiant reads a statement about the couple's commitment.
When the pouring of the sand begins, the officiant or the couple describes the process. For example, as one person pours in the sand first, he says something like, "This sand represents my life as an individual meeting your life as an individual." After all parties have poured the sand individually, each pours their sand into the container at the same time and says something such as, "Now our lives are forever unified and our commitment is symbolized by the mixing of this sand."
The sand ceremony represents the unification of two lives into one life that cannot be separated, just as sand, once mixed, cannot be separated. When writing the vows, this theme is the most important element on which to base the ceremony. If either the bride or groom has children, the vows can be modified to include them and allow them to recite a statement of commitment, as well. The vows can also be modified to fit any religious preferences.