Coconut water is another option as the liquid being used in your soap. But because it comes from the coconut and may have a small amount of oils in it I don't recommend mixing your lye in with the coconut water. But rather mix the same amount of water as your lye calculator calls for lye. Then subtract the amount of water used from the total amount of liquid called for as your coconut water.
When using water in your recipe you can take advantage of using powdered milk such as powdered coconut milk. Use this at the rate so your water becomes coconut milk. So your two liquids in your recipe now become water and coconut milk.
The rate for using powdered coconut milk is 1 tbs powdered coconut milk for every two ounces of water, or 1 ½ tsp of powdered coconut for every ounce of water. For soap this isn’t a big issue if you get more powdered coconut milk than you need for the water used. But if you’re using your coconut milk for lotion it becomes more critical to make sure you’re not using more than you need. I also find it easier to weigh out the powdered coconut milk rather than use a measuring spoon. Use 4.5 grams of powdered coconut milk for every ounce of water.
If you’re like me and your recipe is figured into grams I just calculate my liquid amount into ounces and do the math.
For example: If your recipe calls for 385 grams of liquid that you need powdered milk for just divide that by 28. That gives you 13.75 ounces. Then just multiply that by 4.5 to get the number of grams of powdered coconut milk you need to weigh out.
Coconut water is amazing in soap, and the combination of coconut milk and coconut water is even better. Plus it has great label appeal having both of the liquids used in your soap!