“Traditionally most sand mandalas are deconstructed shortly after their completion. This is done as a metaphor of the impermanence of life. The sands are swept up and placed in an urn; to fulfill the function of healing, half is distributed to the audience at the closing ceremony, while the remainder is carried to a nearby body of water, where it is deposited. The waters then carry the healing blessing to the ocean, and from there it spreads throughout the world for planetary healing.”
http://www.mysticalartsoftibet.org/Mandala.htm
http://www.huffingtonpost.com/2014/10/07/mandala-of-compassion_n_5942202.html