Why does eating snow dehydrate you?

According to Survival Cache, eating snow can dehydrate a person because a person's body expends energy to heat and melt the ingested snow. Eating snow is therefore not advised in survival situations.

Survival Cache also states that snow lying on the ground tends to accumulate bacteria that can cause illness. Eating snow has the potential to lead to hypothermia. To consume snow more safely, it is advisable to melt the snow and drink it. In survival situations, it is recommended that any snow consumed is fresh, white snow. If none is available, purification of the snow is recommended after it has been melted.