When you are a Mormon and are fasting can you drink water?

That is a personal choice between the individual Church member and God. Most members of the Church of Jesus Christ of Latter-day Saints (the "Mormon" church) choose not to drink water unless they are drinking the Sacrament water. Most make exceptions if they must take a medication or if they aren't feeling well.

Church leaders have agreed that making your best effort to fast is better than risking your heath. Those who have health problems which make it difficult to fast should simply give their best effort. For some this means they have some water and a simple snack, such a bread or crackers.