Yeah, it's amazing sometimes how that evaporated milk piles up.

If you have full-fat evaporated milk, it contains 6.5% to 8% fat, and you can dilute it with water on a 1-to-1 basis to approximate whole milk and its 3.5% to 4% fat. If it is 2% or nonfat (skim) evaporated milk, it can also be mixed with water on the same 1-to-1 basis, producing essentially 1% or fat-free milk.

If you dilute your evaporated milk with skim milk (on the same 1-to-1 basis), you will be decreasing the fat just as if you had used water, but will be getting twice the protein, calcium, phosphorous, vitamins, lactose, riboflavin, sodium, etc., found in regular milk. That's certainly not necessary, and just involves spending money you don't have to.