I get questions all the time about how I come up with my water amounts. I do not use a lye calc to get my water amounts. I simply use a lye calc to get the correct amount of lye to use.
My standard water used is equal to 2 times the lye. So if a recipe calls for 12 oz lye, I will use 24 oz water. This is even true for advanced swirling recipes. You hear a lot “use full water for fancy swirls so that you have time to play”. I create my slow moving recipes with special mind to the oils more than the water amount.
I can’t stand unmolding soap the next day and for it to be softer than play dough. (This is what you get when using a water:lye ratio of 3:1 or 4:1 plus soft oils such as olive that contribute to a slow moving recipe.)
For recipes high in olive oil and other soft oils (50%+) I will use a water amount equal to 1.5 times my lye. Why?
High olive oil recipes are longer to trace, softer initially upon unmolding and typically take longer to cure. Discounting the water helps with all of these issues. It speeds up trace (though still allows plenty of time to design the soap), makes a harder bar for unmolding and reduces the cure time.
When I am doing a 90-100% castile or bastile type of soap I will actually use 1.1 times my lye. So if a recipe calls for 8 oz lye, I will use 8.8 oz of water.
You should never use less than 1.1 times your lye. Lye needs at least an equal amount of water to form a solution. If you use less water the lye will actually fall out of solution and you will not have properly dissolved lye. I typically add the .1 amount to just give myself a bit of a buffer.
Take care when working with a higher concentrated solution. Your soap will move faster, your solution is stronger which means it could burn fast/worse and keep an eye on it when you initially make it as it heats up faster and hotter.
I prefer ratios and I prefer simplicity. 2 times lye, 1.5 times lye and 1.1 times lye are really easy to remember and figure out.
The amount of water you use is simply a personal decision. There really isn’t a right or wrong but it can effect the way a recipe moves, sets up and cures out.