Hi there!
If you are using evaporated goat milk, it is recommended that you use half goat milk and half water. So if SoapCalc recommends you use, for example, 300 g of water, then you would use 150 g of water and 150 g of evaporated goat milk. Prepare your lye in the 150 g water only. Then add the 150 g goat milk to the oils instead of the lye and water. When the lye and water is ready, you add it to the oils and goat milk, then proceed as you would with any soap.
I always used distilled water when I use water.